You can always find a little bit of everything on Craiglist. It's like the cool, hip, grassroots version of eBay. Jobs, cars, bands seeking musicians, that 1980s-style furniture that hasn't come back into vogue (yet) -- it's all there. Even a McLaren F1 GTR.
The car, which was a BMW factory-sponsored Motorsport race car driven by Nelson Piquet and placed 11th at LeMans, has been converted into street-legal spec for your driving pleasure. The 1996 racer is a mid-engine V12, and while we're not sure what the exact specs of this particular custom-built F1 are, its history would imply that it's hella-fast.
Thanks to Steve for the tip.