I get my plastic sheets for free .... but they are all white.
They are previously used as table top covers "glue boards" and are covered in glue residues and little bits of wood or material that were left behind when the sheet was tossed ....
A large number of wooden items are prepped with a glue that takes about 15 - 20 minutes to set up, and then the sheet is brought back to the working table where the individual items are then pulled off and materials are applied... faux leather, silk, velvet, ect .... the workshop makes jewelry displays and boxes.
The sheets I simply pull out of the dumpster. They don't mind me recycling it one bit ... I also grab the leftover cardboard roll tubes that once held the materials. They are good for rolling up materials when I buy it at hobby lobby or jo-anne's fabrics. They do, however, find it amusing that I actually walk into the store with a real fabric roll to get fabric ...
Heavy cardstock won't take quite the same polish that wood would, unless you soak it pretty good in some epoxy or CA ... not sure how it would look. I know that you can make a form of micarta with it, and that it looks decent, but I haven't done any experimentation in that field yet.
Most people make micarta with scrap fabrics, old jeans, t-shirts, ect ... just watch the dust, as it's definitely not good to inhale.