sjspeck:Gates sells one. It's about 1/2 way down on this page - look for Gates Pole II.
http://www.gateshousings.com/accessories.html#hardware2
B&H (www.bhphotovideo.com) sells it for $550. A friend of mine is a swimcoach and was looking for something similar. We talked about modifying a pool skimmer pole as a more reasonable alternative, it's aluminum, hollow for the coax feed if desired, and could be drilled to accept the swivel mount.
Thanks for the link! Gates housings are so expensive though...I wonder if a cheap one can't be made....
It would be easier for your friend in a pool: angles and lights are somewhat fixed in the sense he is standing on a firm floor. Boats move up and down and so will the camera. Michel Rutzen of Shark Diving Unlimited in South Africa (He is the guy that appeared on the cover of Nat Geographics in 98 with his hand on the nose of a Great White) was thinking of putting wide fins on the casing so that it would be more stable in the water. Michel has taken out many professional film crews and he explained me a bit when I got to go out on his boat. Best money I ever spent...I learned so much about sharks and filming on that outing!