Is neoprene really the only way to make wet suits? I doubt it.

Regulate. A dirty word on HN, surely. Regulate the production of and, possibly, the import of neoprene, etc. Force industries to innovate - I know that's not a dirty word here - in order to sell these goods to Americans. Maybe then America becomes the sole producer of environmentally-friendly wet-suits to the whole of the word.

I think this is the only solution since your proposed solution of just "put the plants somewhere else" is, as you've pointed out, untenable.