Go to a heavy equipment dealer and ask for Lexan, they most likely have it right on the shelf as they use it in a lot of cabs to protect the heavy equipment operators.
I use a bit of bullet proof glass in my shop to sharpen my tools on with the scary sharp method. I use 3/4 thick windshields out of locomotives which they give away when they crack or chip and the FRA makes them replace the windshield.
PS: Yes they are indeed bullet proof because trains tend to make nice targets for teenagers. In my career, we were shot at while on the Long Island Railroad.