That's a new one on me.
I know the Hawken Shop sold some T/C replacement parts of steel, like trigger guard, nosecap, etc. I seem to recall they had a patch box as well. You might check that out.
John
PS In the meantime, I did just go on their website and did not see their replacement patchbox listed at all. IIRC, it was not a direct replacement but a totally separate item that would require a lot of inletting to install. I dunno, maybe Track or Dixie has something that would work?