I guess you haven't visited
www.usplastics.com yet...
I found what I needed from McMaster (polycarbonate) in their sample sheets (1/4).
Note: there are multiple grades of polycarbonate: the glass filled kind is the bullet proof glass kind. I didn't go for it, due to price, but I can tell you that straight polycarb is extremely tough.
There's another site that's been linked here before, for acrylic tubing; they also have sheets. Run a search!