Ugh. It's a Hehr window. I would try a local auto glass shop. Tell them it's a Hehr RV window and give them the dimensions of the opening. You have the advantage of it being a square window, so it won't require any fancy (and expensive) radius corners.
Chances are you'll have to pull the window out in order to disassemble the frame and replace the glass, which means replacing all the fun putty tape, etc.
The only other similar window thing I can think of is when we had a member with an '89 have some vandals break out one of his small windows, like your kitchen sink window. But unfortunately, the frame was also severely damaged along with the glass. I had to replace the glass on a window on a previous trailer, but it was pre-SOC, so there was never a thread on it. It was a radius corner Hehr window and it required a whole new top half glass to a picture window, because the previous owner replaced it with plexiglass that was starting to crack.
2007 T-286SR Cherry/Granola, #6236, original owner, current mileage: 9473.8 (as of 6/18/21)
1997 T-2653 Blue Denim, #5471
1979 12 1/2' MC, Beige & Avocado, #4639
Past Sunlines: '97 T-2653 #5089, '94 T-2251, '86 T-1550, '94 T-2363, '98 T-270SR