I found a local glass shop in Sacramento when I lived there that had "RV's" included in the types of work they listed in their online website. I have one of the big rear windows with the top 1/2 one piece and the lower half a sliding window with curved end at the frame edge. This shop came out to my storage yard (the storage guy who lived there threw a rock from his tire when he was messing around with another vehicle), got what was left of the old broken lower sliding piece, took it to his shop and fabricated a new, smoked, automotive tempered glass piece, and even carefully installed it back into the track without removing the window frame.
It might be worthwhile calling around in your area to see if a glass shop there could do the same for you.