I don't know if there is such a thing. But it seems to me it ought to be possible to relay by radio GPS information to a remote unit that a diver could carry or wear.

It would probably get in a divers way to have a bouy floating and a cable running down to a remote unit.

Hmmm, I wonder what can be found on Google about this.

http://www.google.com/search?hl=en&q=Divers%2BGPS

Anyway GPS data is typically serial port data what they call on boats and yachts NMEA DATA. Anyway the problem with a surface unit, on a buoy floater or such is that it wouldn't follow the diver. So it would only tell where the buoy floater is located, not where the diver is located. Of course if the cable wasn't too long, or there was a way to have a remote by radio where the bouy floater could follow the diver fairly closely on the surface...

I'm gonna check out a few of those links on that google search.