They have them at the dealer in the shop where you get hats and shirts and so forth.
Saw some today in Ft Lauderdale. Only in Silverstone and I think black.
I bought my 1/43 scale E39 M5 on ebay. It is silverstone with black interior. However, I am looking to upgrade to a 2001 model with the matching silverstone interior
your best bet in my opinion is to see your friendly BMW dealer about the range of BMW minatures (no I am not a salesman ) there are models of almost everything to ever have an association with BMW. McLaren F1 LM's, the BMW V12 LMR, Motorcycles, the 7 series Hydrogen vehicle, and yes, M5's in 1:43 and 1:87 scale... that was the 99 range
I got a carbon black with caramel interior, an imola red with black interior and a titanium with black interior, all in 1:43 ? scale, from my local dealer in Greenwich, CT. Try Bill, John or Rich in parts. (203) 661-1725 (Competition & Sports Cars Ltd)