There are some bag-like housings for more shallow depths.
However, if I were you, I would check with subaquatic photo in Salinas (they have a webpage). They fix and sell Underwater photo stuff. They would know if you could find something you need, or what could be modified. Between them and the shop in Monterey (I forget the name right now) that they work with, you have as good a chance as possible.
Keep in mind that at any real depth, you will need a strobe of some sort. By the time you have added that, you may want to consider a Nikonos. If you aren't going to be doing a lot of UW photo stuff, consider renting a camera.