I don't recall what the bolt pattern for the cat flange is like on a '97, but I don't think there are any "commercially available" bolt-in replacements. So you'll have to buy a new cat and take it to a muffler shop and have them weld it in. I think CTA motorsports carries cats, probably SP motorsports, and of course summitracing.com does too.
The main cat is the easy-access cat, so I'd start there. If it wasn't the problem, it's relatively cheap so it's not a huge loss.
Other idea: Ask around and see if anyone has an aftermarket ypipe and see if they'll sell you their stock ypipe's cat section.
