I know Sam Meacham who teaches this down in the Yucatan area of Mexico. If I can get one other student he will put together a class for me. I'm just throwing it out here to see if I can get any feedback.
Here's a video of Sam that was sent to me recently.
Cave Divers Explore the Yucatan’s Underwater World | Wonders of Mexico
Here's a video of Sam that was sent to me recently.
Cave Divers Explore the Yucatan’s Underwater World | Wonders of Mexico