Rear pop out glass?????

[Pyrotechnic]

I'm thinking this may not be hard to make if you REALLY had to have one and couldn't find one. Make a metal frame that fits into the gasket just like the glass did, and then you can do whatever you want from there as far as how the glass/lexan seals,hinges, or latches to the metal.

Come to think of it, you may even be able to take an old slider window, gut it, then possibly use the frame as a starting point.