I would check at specialty plastics stores. Not sure if you have one near you, but we got our standard plastic from Laird Plastics, and I wouldn’t doubt that they have what you are looking for.
Otherwise, you can use clear lexan, and find some sort of vinyl that can be stuck on to it.
You could also try http://www.usplastic.com I’ve purchased all of my lexan from them in the past, they have all sorts of stuff, so it’s just a matter of finding exactly what you want