The rifle has been discontinued. It was out of production when the Thompson Center Custom Shop burned to the ground.
It never came back.

The newer model, the TCR 87 was very much the same but with an updated locking bolt in the receiver. It would handle the more mighty Magnum chamberings.
Barrels were interchangeable anyway. I believe the 83 could (then) be retrofitted with the newer bolt.

The barrels are a pressed and pinned fit into a monoblock.
There were noted shops doing custom aftermarket barrels which come up for sale from time to time. Existing factory barrels can be rebored/chambered for whatever would be applicable. Also the factory barrel can be pressed or bored out of the monoblock.
Although I don't know of anyone building new monoblocks for the system, I can do this and have the tools etc for the work. I'm not concerned about the prospect of burning out a barrel. If I do I'll be fine.

Export of most firearms related equipment has gotten very complicated via ITAR. I have basically quit thinking about it. Too much trouble for me at the moment.

If I can scrounge some dies and brass in the next couple days I'll have something to share here for the weekend.

:-)