OOF!…Just as an outside chance, maybe check with Ben’s Cycles as perhaps there was one or several in the Euro Asia treasure trove…
I used to build the wheels for my teammates. Mavic GP 4s were the standard rim by the mid 80s for us. One teammate in particular, who was not particularly heavy at 150 lbs, got me to build him a set of race wheels using GL330s. Everything worked out fine and he was using them as his primary race wheels for several months. He liked the way they felt enough for him to get a set of GEL 280s and he showed up at my house one evening with the rims and a pair of matching 28 hole Campy hubs (we were all racing on 32 spoke wheels, save for time trials). I expressed my reservations, but built the wheels. He christened the wheels at a downtown criterium. The race was the usual manic NASCAR on two wheels and about ten laps in we were alongside one another long enough for him to tell me how much he loved the wheels. No more than two laps later as we were coming out of a corner, I saw that the field was about to overtake him riding slowly off to one side with a visible bump…bump…as he soft pedaled. It turns out that he went over a utility cover that was a bit recessed and the impact was just too much. Despite all of that, there is NOTHING that feels quite like a set of lightweight tubular wheels with matching lightweight supple tires…I hope you can find a suitable replacement rim…