BMW Canada has it listed on their website as a dealer installed accessory - part number 65410412881
Here is what they say:
"The BMW iPod Interface Adapter kit includes 2 wiring harnesses and an interface box. The interface is connected to the back of the radio and a cable runs into the glove box of the vehicle. The connector located in the glove box connects to the iPod and charges the unit while connected if the vehicle is running" 
