Here I have found recently an interesting german auto-house website, offering a lot of classic cars. There are even several M1s! If it's still functioning and real, it is worth seeing. However the fact that all car prices are still shown in Deutschemarks(this currency does not exist since 1999), makes me doubt that.
Nevertheless if you like old time bimmers, go under "Angebote" and check them. Some look really well-preserved.