Are you thinking oversized muskets with inch bores or so or swivel guns, both fit with a yoke. I think some of the foundries that turn out little cannon barrels make swivel gun barrels but the only wall guns stocked like a musket I’ve seen were custom builds
They don't show a picture. This is how they describe it:
"De Witt Bailey was kind enough to loan us his wall gun to copy. This gun has a 54" tapered round barrel with a 1" bore, it also has a lug on the barrel for a pivoting swivel yoke. Wall guns use a heavy iron ramrod and weigh approximately 34 pounds. These guns are a lot of gun [fun ?] to shoot and they are quite accurate. There is a letter on record that Washington had a few wall guns made up that were capable of hitting a sheet of common writing paper at 600 yards. The Yoke is not included in a parts sets."
If you click that link and poke around on the Rifle Shoppe website, you might find some others. I was pretty sure they had this British wall gun, and I thought they had an American one, but I didn't find it. I didn't look for any others.
Big Al1, if you would click that link to The Rifle Shoppe in my post above, where it says "British Wall Gun," it will take you to a web page that shows all of the parts needed to build a replica of a British wall gun, including the barrel. The Rifle Shoppe will sell the parts individually or as a complete set. I think they charge $495.00 for the barrel alone. Sights and under lugs are extra. If you get the complete set with the lock assembled, it will cost you somewhere north of $2,000.00. Then you need to build it, or hire somebody to build it for you.