i've had work done at brickworx, minisport, morris mania, mini tech and newport..
they can all do any job you can think of on a mini, but they're fairly different
i dont have a single one i go to as my favourites are are pretty far away from my house, but i like to go to somewhere friendly and helpful and not just trying to take my money.
Brickworx specialises in everything for rover late model minis from japan/uk and imports, complies and sells them, they usually always have minis for sale.
Minitech is a garage that has a large stock of 2nd hand mini parts, they usually offer a quote before undertaking any work, and they work on non minis also.
Minisport carries the biggest selection of new aftermarket parts from england,
is the australian distributor of zeemax bodykits, minispares, and
They also always have a few minis for sale at any one time.
Newport was a leyland bmc dealership, but is now a spare parts and service for all bmc/leyland vehicles, while also they have a huge yard full of bmc leyland vehicles for wrecking and parts.
like tim said, they have a full set of keys and probably have OEM parts.
Mini king has a range of off the shelf parts and 2nd hand parts, and they do parts and servicing for other vehicles and minis.
Rhemac was also a leyland dealer,
i havent been there, but they do servicing, engine reconditioning and performance engine building including blueprinting etc, and they work on muscle cars and jap imports etc.
morris mania is a morris specialist and 2nd hand parts dealer dealing mainly in minis and mokes and morris minors, but also 1100's and other morris/bmc vehicles.
this is just my observations, and i may have left out some details, but yea.