The ring gear can be replaced, but the labor & parts may make it less attractive than getting a replacement converter, unless doing it Yourself.
What happened to Yours? As far as the replacement ring gear, Transtar/Recon should have them, but if someone's doing it for You(Shop) they'll
probably have a source. The stitch-welds need cut, the new ring needs warmed up after knocking the old one off, then squared-up and re-welded.
If it is a few damaged teeth, they can be MIG'd up & ground/filed back to form, MIG wire is pretty tough laid down............