I swear I went to all the car dealers. Not just drove to them, but went in all of them too. I had started with a new game after installing 1.68B community patch, because my old savegame would not load in. If I can't unlock the motorcycle showrooms, I can't get the bikes, and do the bike races...
Maybe the game is still expecting the old showrooms, and they aren't there any more? Or are there hidden ones somewhere?