I recently ran across this site for listing bikes/cars for sale. Had never heard of it before...only a limited mention I could find on the forum. Bring-A-Trailer appears to be an auction site for vintage/rare vehicles. I put in a couple of BMW models and saw there were some nice things available...could be pricey with the auction format.
https://bringatrailer.com/
https://bringatrailer.com/