Do you mean repair, or replace?
If repair, what repair is needed?
If replace, there is a 12g Armor steel non-ejector Field grade barrel on ebay right now (not mine). It appears to have been blued over significant pitting on the external surface, and has extensive pitting in both bores L > R.
The 12g field grade barrels did tend to have generous wall thickness so honing, by a barrel expert, may be possible
(you'll need to cut and paste the link)
https://www.ebay.com/itm/205013647623?_skw=l.c.+smith+shotgun+barrel&itmmeta=01J9PV2W0NF1TAVA7CAN8P74WR&hash=item2fbbc40107:g:aGoAAOSwWQ1m9EaK&itmprp=enc%3AAQAJAAAA8HoV3kP08IDx%2BKZ9MfhVJKku58hWiF4VAyV8FWNtrCrpH6Jsf6gdCWPWaDmR5TsWr8RuJlYBaGENFOvJ2MU0BYwlt55Kji8BJJBbps3SIhqGoeX4TCof518MrEme%2Fu3K9WZ29tssdUG44bzPwu%2Bx%2BHhzxbhF36PA3bRH7V03Aym5Md5fLTYTxYSru4Na6Z%2BhRj1mLDXiP65ehY%2BVJ4F8%2BT3h41vDSNMKmAEmNEjapKc1Vh67PIkMGdH%2Fi3rDLa7YUlHDsmJ87SBPoqCIP2KGsRwx3dAZ5MSl6xhfBHys8CCmClqGx0w7r8tbk%2BMJCJmvgg%3D%3D%7Ctkp%3ABk9SR7TAi9vNZA
Small gauge barrels are going to be a real search.
