We used Lexan sheet (in the proper thickness) for the stock material to make the broken fins. It's easy to get, heat workable, and won't propagate a crack like Plexiglas. The fins have a bend in the middle, which we replicated by bending the Lexan in a crude brake made from steel bar and angle iron, using an oxy-acetelene torch for heat. It was tricky. A good glass or sign shop could probably do the bend with ease.