No matter what anyone else tells you, a locksmith cannot help you. You have 2 choices:
1) Take it to a BMW dealer and have them install a new cylinder.
2) Buy the cylinder kit from the dealer's parts counter and code the tumblers yourself, but it's not an easy job.
Either way, you wouldn't get an entirely new key anyway, only a duplicate of the original. This is because the car's EWS system controls the signal from the key to the injection system. If the key doesn't match the stored code in the EWS brain, the car will not start. For every BMW with this system, only 10 keys are made, and 2 of them are issued with the initial purchase of the vehicle. It's a big deal to get a replacement, since the spares are stored at their main facility in Germany.