Atari's early coin-ops all used plexiglass AFAIK (not counting table models like Indy 800 and Football) and didn't start using glass until the early 80s.
I thought EscapePod might have them. They had an original one they sold, but apparently didn't scan/reproduce it?
https://www.escapepodonline.com/collections/cpos/products/vintage-nos-generic-cpo
SuzoHapp has them for $3.99 each but requires minimum $50 order
https://na.suzohapp.com/products/accessories/95-1392-10
Betson currently doesn't have them in stock.
https://www.betsonparts.com/torsion-spring-need-for-speed.html
Zax has them but shipping from Australia is about $35 for 1...
I posted some photos of mine, along with the Star-Tech article from Vol 13, Issue 1, in this thread:
https://forums.arcade-museum.com/showthread.php?p=4100484#post4100484