I believe they get it from across the pond and it took a while for my MB owned dealer to get it too. You should be getting it soon. Sorry does that sound like MB speak?
I had a hard time too. Please see the end of this post. There are a few tips to get it done.
http://www.mybclasselectricdrive.com/forum/viewtopic.php?f=10&t=415&hilit=Vvc
I know...so frustrating. The sad part is that most M-B dealers don't have a clue what a VVC is, how to obtain it, or in my experience - care to find out. In fact, the dealer I bought the car from told me that it must be a "Canadian" thing, which is funny in itself since the B250e isn't sold in Canada.
The dealer simply gets the code through their "Netstar" system, though the dealer's General Manager or Service Manager may only have access to it. The dealer I bought the car from couldn't be bothered to do this for me (after a couple of weeks of waiting for it to happen) so I ended up calling MBrace support and insisted they get the code for me (their first option is to send you back to the dealer).
In my case, the customer service rep at Mbrace obtained the code for me from a higher-volume dealership in New Jersey, and associated it with my account. After that, I simply had to press the mbrace button in the car to speak with a support rep to verify my account details, and an hour later I had access to mbrace features (such as locking/unlocking doors) and my EVaccess app (for charging features) started working.