This may sound like a stupid question, but, why don't you just buy a 97' ITR that has A/C, as in 97' many people opted for it from the factory. Becuase, yes, you can put it in a car, but it's all a lot easier to buy one with it already. Especially as this way you know that the wiring and fitment of everything was done correctly. Nothing beats factory installation.

Also, as far as aftermarket kits, any place that restores old cars will know where to get an aftermarket kit. But, on a side note, usually, that's one of those things you don't want to skimp out on, especially if it breaks in the Cali. heat. I live in FL, and having my a/c break would majorly suck.

Any way, good luck with it,
Aj