I have a S&S housing.. for the tokina 10-17mm, we had to find a lens with a similar diameter, like the canon 17-35 (or something like that, I can't quite remember)
anyways, I got the zoom ring for the canon lens and it fit on my lens.. try to find a lens with just a slighly larger diameter than your lens, and the zoom gear should work...
they come with small pieces of rubber that help the zoom gear fit tight.
someone at S&S might be able to recommend which zoom gear to try...maybe buy 2 different ones, try them and return one of them...
just don't do diving with a loose zoom gear! if it comes off it will scratch the inside of your port, this happened to me
scott