Plastics supplier?

Hey we are first year robotics team and I’m looking at the r9 rule that says “ R9> A limited amount of custom plastic is allowed. Robots may use custom-made parts cut from certain types of non-shattering plastic. It must be possible to have cut all of the plastic parts on the Robot from a single 12” x 24” sheet, up to 0.070” thick”.
Is there a specific place for us to get such plastics or is there no specific way to source these such parts. sells sheets of legal plastic on their website. Highly recommend checking them out.