I make some motorcycle accessories from Kydex and I always get my sheet Kydex from Knifekits.com. They have a great selection and the best prices on the net. Of course, if you're only buy one or two square feet, the shipping is almost as much as the Kydex itself. I'm going to be making a few holsters myself, and I bought everything but the Kydex from Tandy leather. They have a store near me, so I didn't have to pay for shipping.
Yes, Kydex is EXTREMELY easy to work with. Just go get a heat gun from the hardware store and you're set. You can also heat entire sheets in your ovento soften them for forming. I usually just lay the sheet on a flat surface and run a heat gun over it until it softens to the point I want it. (Also, make sure you have some heavy gloves to protect your hands from the heat.) You can soften it just enough to take a bend or you can get it really soft so that it will conform around almost any curve. Be conservative with the heat, though. You can always reaheat it and add more bend, but once you've actually stretched out the material, it's hard to fix a mistake.