Finding 1985 sliding windows will be difficult, but if you find a window (as in the glass) of a different length but the same side, you can probably use the glass in the frame that you have now.
I was checking, and this Dutch company that I used before, has a sliding window glass pane, the front one at the right side they say:
https://www.car.nl/_404_w_4090__GB_1
Struts for the pop-up roof, I would try and get it sorted at a camper building company, otherwise try as GPW says via lengths on Ebay.