You can find filters at autoparts stores made by the same companies that make filters for BMW, but you have no guarantee that they are built to the same spec internally. Physical dimensions being the same and a cross-reference number doesn't guarantee that they use the same filter media.

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2007 X3 3.0si, 6 MT, Premium, White

Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue