Didn't see anything that would work on Electrodynamics site, I've used one of their vacuum formed sheets that was included with a lighting kit I've purchased, but they don't have what I need.
Sysiek, if stretching over my existing piece works, that would be perfect. I've read about vacuum forming plastic canopies, but it seems more involved than just heating & stretching & requires an oven (other than the one my family eats from). Have you tried it before?