I have several 12 gauge rifled barrels for sale that were made by E.R. Shaw. They are new barrel take-offs that came off of Savage rifled shotguns. These are big enough to make sleeving barrels out of for converting your 12 gauge smooth bore into a 12 gauge rifled gun. I will take $200.00 for a pair of them and I will ship them to the lower 48 states at my expense. The twist rate in them is one in 35 inches and they have fairly deep rifling in them.

I also have rifle and slug gun top ribs for sale, these will work on guns with 22 to 26 inch barrels. The cost is $100.00 each and $10.00 shipping. If you buy a pair of barrels and a rib together, I will send them all in one package at my expense to the lower 48 states. That's three hundred dollars, delivered to you, for a pair of new rifled 12 gauge barrels and the top rib. That will go a long way towards getting you a 12 gauge rifled conversion gun built.
Bob