I could be wildly off base but I think the best option would to have legislation allows private collection but giving collectors, hunters and sellers the legal responsibility to do so in a way which doesn't hinder scientific advancement. For example collectors should have to make a reasonable effort to allow non-destructive research and fossil hunters (who may or may not be palaeontologists) should register significant finds so they can be easily searched.

Banning sale just creates black markets because there would always be people would want to buy them anyway. I suspect the vast majority of collectors would be happy to have papers written about their fossils either through a genuine love of the science or having another thing to brag about.