I picked up a Russian made Zenitar 16mm fisheye on ebay a couple years ago. This also comes in an Olypus OM mount so it prob. doesn't help you much... I think Steve's option would be better for you. If nothing else, you can make your distortions digitally with the computer.

http://cgi.ebay.com/NEW-FISHEYE-ZENI...QQcmdZViewItem