May have been stolen, but the glue that holds them to the base does break down and they come off on their own. It's item 9 for the full roundel assembly including the mounting base. Google part number to find the best price. Note, if the plastic mounting base is still there and just the badge is missing, Google on 70mm BMW badge and you can get one that will stick onto the base.
http://bmwfans.info/parts-catalog/E8...ont/#7044207_9