For parts I would check with D and R marine, Mass Marine and IBXBoatworks.com. If you're not familiar with D&R, the owner, Rudy, was O'Day's parts manager. He has since kept our O'Day boats alive by working with the original suppliers that O'Day used. The IBX and Mass may have some salvage parts you're looking for.
The windows are quite brittle after 40 years of UV abuse. I have had some success glassing the pieces back together. If you're lucky, only one or two medium or large pieces will break off. Line them up with the window, tape it in place from the front, add some cardboard to the front if more support is needed, fill in the backside of the area to be repaired with resin, when it dries sand off any excess until you can't feel any bumps or voids and finally mask and paint the frame. Masking the frame is by far the most difficult part. You really need to get the tape between the frame edge and plexi as much as possible. I have a box of chipped window frames if you're looking for some