I was lucky enough to get hold of a NOS backglass for my Fireball as it came with a plexi repro.
I have to say the graphics on the Fireball repro plexi were superb, top notch, but I prefer an original screened on glass. Don't hesitate to buy one if your original is rough.
Apparently some of the Fireballs that were exported were shipped with plexiglass when new, does anyone have a definitive answer on this?
Some other games were produced with plexis, one reason some manufactureres may have discontinued plexis is some people were reported to have burned holes to access the credit wheel!
I guess it's possible.