I would say that SRQ Hoyas in Florida and Kratuz Greenhouse might be your best bet. Hoyas are just not popular enough to find a good selection from anyone but a specialty grower.
Also buying a plant in a 3-4" pot does not necessarily mean it will be a tiny plant. Those huge mature stock plants you posted photos of would be very expensive indeed.

If you get the urge to travel out of country then Thailand would be the best place to go. Bangkok and the surrounding countryside house a massive number of specialty orchid growers who also grow Hoyas and a few growers even specialize in Hoyas. You would need an import permit before you leave but otherwise shipping the plants back to the US is not a problem. You may be able get all the paperwork in Thailand but I am unsure of the rules in that case.

Mike

You know, Mike is right on target (as always) but I would just like to add the following:

1. Your photos are awesome. I very much enjoyed browsing them.
2. You might just try visiting these vendors anyway and simply asking them which Hoyas grow aggressively. You can have a large plant on your hands in now time if you choose with that attribute in mind. I have several from Joni that turned into monsters over the winter despite arriving in 4" pots. Also, it is super fun just to see their 'mother' plants. After visiting SRQ, I felt this sense of deep satisfaction at just having seen certain plants with my own two eyes, even if I couldn't take them home. It is hard to describe, but it was a truly satiating experience. I was just glad to see them living and prospering in a safe environment. :) lovelovelove
3. You might just want to sit on this impulse for the time being. Tastes change as your experiences with a plant species ferments. :) You might find that 3 months from now you would trade a mammoth obscura for a tiny 5" vine of ignorata. (YES I AM STILL THINKING ABOUT IT!)

Thank you guys so much for your input! : ) Mike, it didn't occur to me that 3-4in could be a reasonable size - but SRQ's hoya are shipped in

and are much larger then I expected! (I actually wasn't aware of SRQ at all.) Though I was so hoping for a larger plant then I could purchase online. The Thailand information is helpful too :) though not somewhere I'm brave enough to venture yet! (Still young!)

Ghost that's good advise. My wishlist consists of all fast growing, fragrant and easy blooming hoya. haha. But it may be that i'll become more fond of slow, stubborn (but still fragrant!) hoya. The later of which is more rare, and worth a trip for. In fact SRQ has a $10 March sale on hoya... and most of the sale items are the fast growing varieties already on my list.

As Mike says, you can buy GENUINE mature plants, at a hefty price (mostly because of the shipping, tbh). If that's really what you're after, then you might try ebay and check out the plants of greenthumb3000 or other such vendors.

What I would be more wary of is judging a Hoya's maturity by the pot size specified. You can get EA Hoyas in a large 8" pot, but they really are a bunch of rooted starts (as pointed out in this thread) not in the same league as the photos you shared with us. (But they'll get there, someday!)

Joni @ SRQ just recently changed her pot size, but the plants are equally well established as what she'd previously been selling in 4" pots. I tend to find that the health quality and selection of these plants outweighs getting a greater number of starts. She has been holding monthly $10 sales recently, with different plants featured every time. You can really get some good deals and these plants tend to be on the fuller side versus some of her rarer plants, which she offers as soon as they are well enough established to travel.

She used to also sell bigger pots of some plants and they'd go into the $10 sale section, too, but I can't find them on her site atm. You might inquire with her about it, though. Don't be afraid to talk to Hoya vendors directly. They are a good bunch. Because it's a smaller community, it's often easier for them to connect with us.

Your final option is to get big cuttings! I know this sounds crazy, but some of the cuttings I've received in the past amount to a pretty darn big plant. The typical size of a Hoya cutting is, of course, 3-4 nodes, but there are some vendors who will ship larger sections, at their discretion. And you can always stick around here, make some good friends, and before you know it, there will be some sweetheart from a southern clime, who thinks you're worthy of a big hunk of a Hoya that grows like gangbusters for them. Everyone here is astonishingly generous once they get to know you. It's all about putting in the time.

Also, Hoyas do not have to be huge to flower (in case this is not self evident). Because Hoyas are usually propagated via cuttings, they benefit quite directly from the maturity of their parent. You will be astonished how many cuttings and plants you receive with peduncles already there, in which case you could have blooms on your hands a month later even if it's in a 2" pot, or freshly rooted with your own two hands.

Whew! I think I'm about halfway to a book. Sorry about that!

Wow you did have an essay going haha. But I didn't even notice until you mentioned it! (something similar to 'time flys when you're having fun,' ?)

Thanks for the direction, greenthumb3000's Hoya are quite expensive. I think part of the fun of buying mature hoya lies in the selection :) which isn't quite the same online! (I'm a kid in a candy store when I go to our local nursery! Boy friend takes me there when I've had a hard week )

Good to know that SRQ has monthly sales, I thought it might be a spring only sale. I'll keep an eye out for her larger plants, though I've started to think that buying a grown-up hoya would ruin the fun of it all! I form an attachment to plants that i've raised! I can't wait to get more though C:

Large cuttings sound like an option. Though I had heard it puts extra strain on the newly rooting cuttings, when it has to support a long vine of leaves. But I'm not too sure about all of that!

I can already tell that everyone is so kind :) I have been a part of many non-plant forums, but it isn't anything like the community here!

They are very expensive. But in cases of uncommon super fussy offerings, they're surprisingly reasonable, considering the time it would take (at least in my conditions) to grow to that size.

I'm like you, though, I really prefer to see a plant go from small to big under my own care. You really get to know their individual personalities.

If you haven't been shopping around for long you might be surprised how much the selection changes over the next few months. Many vendors are only just now starting to post items. Everything just explodes over the summer months. Hoyas you've never seen before will be popping up everywhere.

There really is a diversity of opinions about the ideal cutting size to root. Some people insist 1 node cuttings are the best. Other people believe it is best to root larger cuttings and simply pin a section of the vine horizontally along the soil, capitalizing on the fact that it will send down roots from multiple nodes. Personally, I have tried all kinds of methods and the only thing that seemed to have an obvious effect was how stressed the cutting was in transit. My point being you can easily root a large cutting if you want to, whether it's the 'optimal' way or not.

You know, I've been on other forums too and never experienced this kind of atmosphere. I suspect, though, that it's because our plants are loved ones to us and we are in an environment where people want to listen to us yammer on about them. I bet if I went to a cat forum it would be the same. You want me to tell you about my cat?! I will tell you about my cat x1,000!!!!!! Wheee!

And also, how bad can a person be who wants to spend their time and money nourishing lifeforms that they can't eat or even show off to their 'normal' friends.