Have you tried Mayfair Amusements for a used glass?
http://www.mayfairamusement.com/backglasses.html
Are you on Facebook? Try posting in these Facebook groups:
Pinball and Arcade Parts only
Pinball parts and machines wanted
Mid-Atlantic pinball and arcade enthusiasts
Md-dc-va Arcade and pinball
Try posting in this forum
https://pinside.com/pinball/forum/topic/whats-fs-in-maryland-right-now-maryland-fs-thread