Sadly, there is only one independent shop that I know of in the state of MD, and he doesn't really want to work on MINIs at all. Has even copped a bit of an negative attitude towards them, and can be difficult to work with. Also, his prices tend to be quite high. Don't even mention DC Metro MINIs to him, as he became disenchanted (to be polite) with the club years ago.
Having fore warned any potential customer, his name is John Behe (pronounced beehee), and he owns Behe Performance, in Glenwood MD. Here's the link:http://www.beheperformance.com/