There's a few suppliers of rear screens. Assuming you still have the zipped in window. I bought one around 10 years ago. It zipped in easy and stayed nice ever since.
But I recently took it out because a part of the roof stitching came loose. I stitched up the roof but couldn't find the zipper/slider thing. Tried other zipper/sliders but none were a good fit.
Eventually I managed to get it zipped back in but then lots of other roof stitching started coming loose.
Basically, 25+ year old roof and the stitching is ripe. New back window won't fix it. New roof, for me at least, is the only solution.