http://www.thomasnet.com/wisconsin/plastic-sheet-sheeting-59970400-1.html If you are using this for interior pieces, try to get sheet that has NOT been rolled up for storage or transport. You may have trouble getting it to lay flat. I, most often use 1/8", which is highly unlikely to have been rolled.
If you are going to use it for interior door panels and etc, look for a sing supply co in Milwaukee or Madison. I have used this in the last two interior I helped with. It comes in 4'x8' sheets and is about 1/8" thick. This is pvc sign material and is about $30 @ sheet. It is easy to cut and can be bent by using, carefully, a heat gun. If you PM me I can give you more info, rj