You use Clear Jel for pie fillings. Pectin is for jams and syrups, not pie filling.
Clear Jel is ordered online, not in stores, other than a very few extension offices, one cake decorating shop here has it, and some Amish stores. It is cheaper for me to order online than at the cake decor store.
It is a specially modified corn starch, like the commercial industry uses in foods. Read labels, it is most everything. It won't break down during canning, unlike cornstarch, flour, or tapioca. It is the only thickener the USDA recommends for pie fillings. It holds up to freezing, too.
If you use pectin, you will have jam, not pie filling. Pectin is from citrus peels or apple pectin, etc.

It's frustrating that ClearJel is so difficult to locate. I ordered 8 pounds online because I got a price break. It doesn't deteriorate, and I now use it as my preferred thickener for many things.

You will see more and more canning recipes that call for ClearJel. It's the only tested, approved thickener for pie fillings, but I also noticed in the most recent Ball Blue Book that a mustard pickle, which previously called for flour, now calls for ClearJel.

Carol

Here sometimes at the United Grocers/Cash and Carry they have 25 lb. bags of modified food starch. I think last time I saw it there it even said Clear Jel, but I am not 100 percent positive. If you had someone to go in with you, it may be worth it. It was a bit over $30. Cheap per pound.
Here they sell to mostly businesses, but they never ask for any ID, no problem for me to walk in there, but you do have to use cash.
I paid $3 something for it online, but now the place sells it for $3.99 a lb. You just have to search online for the best prices is what I found.

"...where can I find pectin..."

Sure Gel and Certo are brand names for pectin. I'm not advocating them for pie filling, just answering your question.

Jim

Just added a bit of 'Thick and Quick' to whipped cream cheese. It was put in a big pan with a graham crust bottom. Then refrigerated. This is an instant starch and helped to make the cheese become quite firm immediatly. The cheese cake will be topped with some cherry pie filling. Both are sweetened without sugar. Clear Jel is a modified food starch, much more stable compared to regular corn starch. The Sure Jel is a brand name for pectin. If you want a syrup and don't want all the sugar and cooking, use a little Clear Jel instead. If you use a lot of Clear Jel, the result is like a 'gummy bear'. In either case, Clear jel can break down if the acid in the food that is to be thickened is high. There are several other types of food starch, specifically for reheating, high acid, freeze/thaw cycles, and a few more conditions.

SO I can use either Sure Jel or Certo for recipes that call for pectin?

Harriet, if you check your jam or jelly recipe, it will say either dry powdered or liquid pectin. You cannot substite one for another in a recipe. Use the one called for. If it says dry, then use Sure Jel. If it says liquid, then it is Certo.
There was a dry Certo pectin sold, but I don't know if it still is. I know there are some pectins that are sold in different area of the country.
Here is a good link with info about making jams, jelly, etc. One of the best lessons I know of. Shows pictures of the packages of pectins, too.
I just order my pectin online now, and going to stick with Pomona's Universal pectin. I think the stuff would gel water. It is dry pectin, and it is done a bit differently than regular pectin. Sort of a trial for me at first to get it to not lump all up. I figured out for me it works best to heat 1 cup of the juice called for with the Pomona's, then blend with the immersion blender, then add to the rest of the juice or fruit. I tried doing as they said and mix with the Splenda, but it lumped up too much. You can use Pomona's for any kind of thing, sugar, no sugar, Slenda, honey, stevia, plain fruit w/o sweetener. It is really cool stuff for me. The jams and jelly turn out sort of cloudy, not clear like regular pectin, though. Not as pretty in the jars, but oh well. It has allowed me, being diabetic, to make some great things for myself. My family and friends are telling me the like the no sugar stuff with Splenda better than the regular sweet stuff with Sure Jel. You taste the fruit, not just all sugar. More fresh fruit tasting to me.
I think Ken will agree. Some of the others, too. Annie doesn't like the Pomona's, though, if I remember. Pomona's is a lowmethoxyl type pectin. You order it online from Pomona's or other places. Pomona's sells in bulk. It is different from the other lowmethoxyl ones you buy in the store, though.

Here is a link that might be useful: Making jams

I buy the Clear Jel in quantity from the Amish, and last time they gave me a "substitute" that they were using - forget the name but it was similar - kind of like a knock-off to Clear Jel. Worked fine. Sure wish I could remember what it was. Doesn't make much difference to me, though; I now have 50 lbs. of Clear Jel in the freezer. Think it should last the rest of my lifetime!

Yes, readinglady, I use it for all kinds of thickening too. Doesn't thicken up that Apple cinnamon syrup as well as I'd like, though.

Using Clear Jel in jams.

Here is a link that might be useful: Using Clear Jel

Thick and Quick is also thickener I used to make some cheese cake. Because creamed cheese tends to weep and soften when whipped, I added a couple of spoons full of the no cooking Thick and Quick and it sure didn the trick. I bought it from KItchen Krafts

Here you can get Certo brand in either a dry or a liquid.

Zabby

Zabby, we used to get both the dry and liquid Certo pectin, too, but I only see the liquid now. The dry is either Sure Jel or MCP. I don't use the MCP because it calls for adding corn syrup along with the sugar. The corn syrup is more expensive. I don't always have it on hand.
Now I am using Pomona's pectin mostly. I will use up the Sure Jel and make regular jams for my grandson. We don't want to give him the artificial sweeteners. My daughter prefers it that way.

I have a roquefort salad dressing recipe that calls for clear jell. I have never been able to find it. I thought that it no longer existed as this is an old recipe. Linda lou, would you share your online resource with me? I dont need 10 lbs. I'm hoping that they make it in jar that can be stored. I was using certo with uneven results. sometimes too thick, sometimes not thick at all.

Amazon sells it by the 1 pound for about $3.50.

There ia also an instant one that doesn't need cooking. Its used in most instant puddings you see in stores. As a thickener with no actual carbs or starches, xanthum gum can also be used. They use this in many oil free salad dressings. It has not taste and thicken liquids quite fast, without any heating. Not sure if it could be used in home canning though. Kitchen Krafts also sells a product that is instant as well as cooked modified food starch. Then there is Pomona..

Actually xanthum (or xanthan) gum IS a carbohydrate. It is a polysacharide (polymerized sugar), just as starch is. Xanthum gum can be used in making low gluten or gluten free baked goods. Also, a very small amount of xanthum gum is needed to add viscosity to sauces and dressings. It works similarly to modified starch and is sometimes used in combination with starch.

Jim

From what I read about the gum was it was an organic product of some kind, like a living cell that had been dehydrated. A quote from another web site: "made from the outer coating of a laboratory-grown micro-organisism called Xanthonomonas campestris". The info never pointed to any sugar or carb, but did indicate that it was used as a substitute for gluten.

I order mine from Barry Farms online, but there is now $3.99 a lb. I know some places you order products from do not charge as much for shipping, so it all depends upon what is cheaper for you. I get really good service from them, so I stick with them.
You need the regular Clear Jel, not instant when canning pie fillings.

I have salad dressing recipes that call for pectin, never had one that called for Clear Jel.