I was talking to a guy last weekend who races in the supermoto series and he was saying he rides a Honda CRF450.

Here ya go!
http://westslope.craigslist.org/mcy/3049600923.html

Also look at these. The 525 has the same chassis as the 450 (at least for the EXC's), 5 pounds more, and more hp. I have no idea how it's set up differently between the EXC and SMR. Plus, 6 speed tranny.
http://www.bikez.com/motorcycles/ktm_525_smr_2005.php