I don't have any "regular" suppliers of carbon fiber, but rather look at several outfit online to find what I'm looking for. Personally, I don't use carbon fiber unless its specifically ordered on a knife. My reason are that its terribly nasty stuff to work, dulls any and every tool that touches it, and just finishing out a handle will make your shop look like somebody threw a full container of black baby powder into the air, and it settled everywhere.
Those are just minor compared to the health hazards. Having already had TWO lungs surgeries, and finding that those were caused mainly from "shop dusts", its most certainly a material which REQUIRES you use a GOOD respirator. We're all "ten foot tall and bulletproof", until the Doc tells you you have tumors in your lungs! If you must use carbon fiber, do it sensibly, and protect yourself.