Take the part number to BMW and see if they can order it if that's the route you want to go. The guys in the parts department are useless. Well in cape town anyway. Personally I wouldn't do that. If you're only replacing the speakers what are the chance of them ever finding out and if you have to use an amp make sure its hidden. I doubt they will even car if they find it. You will get far better bang for your buck going aftermarket.
I've ordered window trim for my E90 before, first they send an e46 trim, then the wrong side E90, then 3rd time lucky they were right.
Ordered dust covers for my E90 xenons, they sent the halogen ones first.
Had a little rear bump had to order a new taillight the sales guy was adamant to the panel shop that there was no such thing as a "blackline taillight" and there is only 1 type of taillight for the E90. I had to get these morons the part number so they could order it.