Try looking at McMaster Carr, they sell all kinds of materials and will give a discription on it properties. Then after you find what you want you can order it through them or go else where. When I need plastic I either order from them or a place called Midland Plastics, there in the midwest and might have a distributor near you.
I use alot of Delrin, it may be a little more expensive, but its good stuff, machines well, wears well, and holds its tolerances pretty good for a plastic.
http://www.mcmaster.com
http://www.midlandplastics.com