Hi Corey,
I did a google search for "polymer lexan" and got this place...
http://www.polymerplastics.com/transparents_lexan.shtml
amongs others......they are in reno nevada, but there should be a supplier closer to you.
The margard is usually about twice the price of the regular stuff.
If you know anyone who is a distributor for Allstar, they carry it in precut sizes, although the sizes are weird and can give lots of waste.
Lexan is the brand name for this stuff made by GE. other companies make similar stuff, and margard style polymer under different names, but just as good.