Here is another option that will work with a 10mm spacer effectively giving the 9.0" wheel an offset of ET31.
LTW5 Lightweight Alloy Race Wheel - 17 & 18 inch (3 Series)
Looking for a super strong, ultra-lightweight wheel in a 17 or 18 inch size for your 3 series? Look no further! These are the perfect track or street wheel for fitting wide rubber under your car. At just over 16 LBS each on 17" and 18 lbs for 18", you'll have a hard time finding a better performance wheel for the money. 41mm offset, flow-formed for superior strength, and fully tested for impact and crack resistance. Available in 4 sizes, and FOUR finishes; silver, anthracite, gloss black with machined lip, and flat black (new!). BMW roundel center caps are also available.
Recommended tire sizes:
17 x 8.5" (16.0 lbs) - 235/40 - 245/40/17
17 x 9.0" (16.6 lbs) - 245/40 - 255/40/17
18 x 9.0" (18.0 lbs) - 245/35 - 255/35
18 x 10" (19.0 lbs) - 285/35 ** rear fitments only **
Part #: LTW5-WHEEL
Options: Choose wheel finish SilverAnthraciteGloss Black w/ Polished LipFlat Black (17x8.5 only)
Also TCKline has Volk custom make their TE37 in a 9.0" ET40. With a 10mm spacer you have an effective ET30 offset.