There's a few shops in st Louis woth stuff. Nocturnal Motorsport/JDMhookup has tons of 1JZ and 2JZ stuff, same with Adrenaline and Speed and Sound. Dewey, Dan, and Omar at JDMhookup are all pretty straight. That said, your best bet is to buy parts online. It will ne cheaper and easier than going to a local shop
We used to have one almost every year in St Louis. Most people have gotten rid of their supras but we used to do it in the fall and meet at Queenie or a park that had a nice lot. There would be a couple dozen Mk3s and a few Mk4s and Mk2s. We would bring at least 3 or 4 from our shop.
Or we would organize all the Mk3s for other shows and have a group cruise in.
As far as shops that are still around, that have knowledge of the Supra, Speed and Sound is the only one I know that actually owned and built a Mk4. They did a few 1j swaps into Mk3s too.
Not sure, its a built 1jz that apparently made 750whp... I know they still have the motor and ate still around. I know a guy that works there and they brought all their shop cars put for import face off in September's. They're better than they used to be