i think you get the Toyota GT-One from getting all gold on Super License, the R390 LM as a bonus car for getting all golds on one of the license test and the AMG......never even heard of it
BTW, the GT-One road car is ugly...especially the back. The race on is though
the mercedes amg was a german touring car or fia gt racer that was not put in the final version. you need a gameshark to unlock it, if you have a dex drive you can search the net for a gme file that has it