I don't know if you'll find rims that have the right offset to fit your M3 from the dealer. The only thing I can think of is maybe some 5 series rims. I don't know the exact offset of the rims for a M3 or 5 series so I don't know if they will fit. But if they do than I sure you dealer would be happy to change rims for you...for a price. I inquired the same thing when i was getting my car and the dealer told me they will buy back my stock rims and use the money to purchase new rims from the dealer. But you will have to put out money. It was going to cost me $300 just to swap rims that were the same size. It didn't seem worth it to me.
Just go aftermarket and sell your rims on ebay or something the offset the price.
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