There are a few schools out there that just do underwater welding training. But I believe that you have to have commercial dive experience, or at least been to school for commercial diving, but don't quote me on that. The one school that I recall right off hand is Hydroweld, I believe that it is in south florida. There are several school overseas that also teach wet welding. I've been wet welding for 5 years in the gulf of mexico. I do maybe 8 to 10 wet welding jobs a year. As far as the possibilities, if you're not going to become a commercial diver, I don't think that you'll have much success. Good luck.
Chuck