They aren't cheap, but do add a completely new functional layer over the horrible Mercedes system. Certainly cheaper than chopping the car in for something more dynamic which would have been the option.
It came from http://www.ckmcardesign.com/ but you can buy them direct from China on Aliexpress for a bit less, but you get chinese support with that. I'm not too far from you up in Norwich if you ever want to see one.
