E36 is similar- you have to keep checking with the dealer, as they get no warning either...
Parts go in and out of stock (seemingly) randomly. The adjustable splitter for the M3 LTW and M3 GT (in Europe) goes in and out of stock all the time. The splitter itself is usually in stock but the brackets going up to the bumper are not. One company in Latvia or wherever is reproducing them it's so sporadic (lots of racers use the factory splitter).
Realoem can help, but the pricing and availability there is not 100% accurate.
(PS the Gr. A and Gr. N parts list is in the "classic>1928 motorsport" area or something like that. Hidden in plain sight, not found under E30 or E36...
