I think you have the right era identified. My '85 Rockhopper still rides great and amongst it's many incarnations, it still works extremely well for road and off-road touring, with a variety of loads. Most of those early mass-market frames had sufficient brazings and many are likely to have survived- the thick tubing was designed to endure our hopeless off-road skill levels, wasn't it?

good luck with the search.

oh......and did you fix one of those babies yet? (my Rockhopper handled the experience better than I did;-))