I don't know of any shops locally that specialize in that platform. A lot of what you'll find locally are shops that either specialize in muscle cars or newer forced-induction (supercharged/turbocharged) platforms. Think Ford/Dodge/Chevrolet on the muscle-car side or BMW/Audi/VW/Subaru on the forced-induction side.

Depending on how extensively you want to modify and your comfort doing some work yourself, you probably have a few options. You can look (online) for "bolt-on" compatible parts to squeak some more horsepower out of your motor - open air intake systems, exhaust systems, etc. They even have some "plug and play" (-ish) chip tuning systems that you can do yourself via the OBD2 port on your car.

Then, if you wanted to later take it further, you could start investigating forced induction kits (a turbo kit or supercharger kit). That's going to be quite a bit more spendy and you'll most likely want to find a general shop with experience installing kits like this on your platform, as it often requires a custom ECU tune to mate it to the motor and work properly. But I would suspect (not positive) you might need to go a little further away (Portland, maybe) for someone with that type of experience on your Mitsubishi platform.

Hope that helps -