I know someone who works for BMW worldwide who has contacts at M division. I asked him how I would go about getting the GTS wheels for my order. He contacted M division and BMW individual and they said the following:
Black wheels for the M3 are available via BMW Individual. Option 2MT in Black high gloss and Option 7MA (Competition Package Wheel) in Black matte. Price additional to the wheel 241,-€ Ex-fac.
He said my salesperson should contact BMW Individual directly. Unfortunately, the dealership I worked with didn't care enough to make it happen for me. Sometime's it's all about knowing the right people. I hope it happens for someone else since my chance fell through.