I don't know where to get one now, but we (Team 116) used one for the 2001 season. It was my own personal steering wheel, which was a Mouse Systems BogeyMan Racing Wheel. Here is a photo of it from a post-season outreach event we did that year with Dean Kamen (and, of course, Dave Lavery) at the U.S. Department of Commerce, and there are a few other angles in the same album:
http://www.invisiblerobot.com/roboti.../p2148842.html
UPDATE: Looks like one is available on eBay at the moment.
Link