Personally i just use a good independent
But with the exception of Subaru most good main dealers now Mitsubishi in Particular (25 % of their UK parts holding is for imports) are geared up to service and supply parts for imports, Most now have all the CD's for parts, and servicing is no different to UK Cars, sometimes though some garages may not have all the software to read all fault codes though.
Imports have been around now since 95 in the main market, so all this scare mongering about Parts supply issues and servicing is untrue, It was a case the Dealers over here had no option but to get on the import bandwagon, this in return is why insurance is no longer expensive either