To be entirely honest, I have YET to find a single part for this car I can't get from my job for the right price. A large amount of parts I actually just take from the junkyard, or buy from rockauto when they're correct. If you don't see the part under an XR2, you look under 1988 mazda 323 turbo, the part is almost always there.
Performance parts are pretty simplistic, nobody makes kits, but making your own is so simple there really is no point. The whole front end of the engine bay is easy to play around with, and a decent exhaust system can get bent for a cheap price. You can purchase a boost controller to up the boost to a better number then the starting 5-6psi, and if you buy the rocketchip, made by rocketman here for <$200 your car can run 15 psi easily. Auto stores sell the vaf adapter for the air sensor, the air filter I found that works is the short ram cone by spectre, it just clears the coolant reservoir.