Not that it's too difficult to make a scuba diving pose: get a laying pose, adjust arms and shins, and you're done :-)
When I build this kind of poses myself, I tweak the dials for around a minute only, it isn't really so difficult expecially if you can find some references (not too hard to find, too...).

Then if you want some "posing underwater" poses, as far as I could see, sometimes a sitting pose lightly tweaked can do the job; some models can pose as they're in open air, standing and so on...so get a standing pose and made the environment :-)