The guy probably wasn't lying about it coming off an SL55. I was looking for one for my XF in black and ran across this auction.
http://cgi.ebay.com/ebaymotors/Cars-...em260250017599
Now all I have to do is figure out how to wire it into the ignition circuit and get it so it will not engage the starter unless the engine is off and the clutch is depressed.