You can try ebay, that's where I got mine. His price is pretty reasonable, he has purple haze, american beauty, and white guyute. He offers 2 cuttings per auction and he also have combo cuttings of the 3 mix.

http://www.ebay.com/itm/2-RED-2-WHITE-2-PURPLE-DRAGON-FRUIT-PITAHAYA-with-9-inch-CUTTING-3-in-1-/150974261856?pt=LH_DefaultDomain_0amp;hash=item2326c46a60

I have 9 varieties, of which I've only had Giant Vietnames & Voodoo Child

Voodoo Child
Giant Vietnamese
Physical Graffiti
Yellow
Thai Red
Purple Haze
Phoenix Red
Arizona Purple
American Beauty

Hi Rodney, You've got quite the interesting line up of dragon fruits collection that I haven't heard of. I'm just starting growing dragon fruit and would love to add a few more varieties. If you can spare some cuttings and send me some, I can pay shipping?
email @ kimchitop@hotmail.com

Thanks
Seng

I purchased purple haze from that same ebay vendor, they arrived in good shape, a Zamorano i was able to get locally.
and I have a Makisupa that has made its way up the side of my 2 story house and made it to the roof. it hasn't fruited yet.

I heard the the variety "Delight" is very good, and Haleys Comet, is a big one that can get up to 2lbs.

Just make sure they get sunlight, warmth, they like fertilizer, and even if they are cactus, these grow very fast, and do like being watered often, but must be well drained. fungus / rot is their worst enemy.

In the summer, I have seen mine grow an inch or more a day !

other tips, Do not use treated wood as a support, DF have aerial roots, and can pick up toxins from it. also you want to create a support so that the stems can droop downwards, vertical growing stems I have noticed wont grow fruit.