Justin,
The late Ketland lock may be your best choice for a commercial lock. The Ketland trade pistol below, which dates to the 1790’s, has a lock that is 5” long and ⅞” high or about the same dimensions as the Chamber's late Ketland.
The Ryan & Watson lock that JCKelly showed is very typical of locks found on trade pistols of the period you’re interested in. The least expensive ones had no bridles while some of little higher grade did have bridles. Unfortunately, none of the commercial lock makers today offer a comparable trade lock.
Back in the 1970’s, Frank Straight started a company called Green River Forge. In addition to mountain man clothing and paraphernalia, they offered a reproduction Northwest Trade Gun, a rifle they called the Astorian, and a replica trade pistol called a Hudson’s Bay Factor’s Pistol. The latter was supposedly copied from an original Barnett trade pistol in Straight’s personal collection. I bring this up because Green River Forge used a modified CVA flintlock on their pistol. The lock they started with was one of these.
The modifications resulted in the lock below. Note the tail has been rounded, the pan was reshaped, most of the cast-in engraving was filed off, and a tumbler safety added.
The original trade pistols were built to a pattern, and even though different makers may incorporate a few of their own touches, pistols by various makers still looked pretty much alike.
I have another trade pistol that has “W & S ROOKE” on the lock. Baily and Nie list a William and Samuel Rooke operating in Birmingham from 1820-1837 and Samuel only from 1837-1839.
The shape of this lock is very similar to the one JCKelly posted, especially the shape of the cock, but it is a more expensive grade with pan and tumbler bridles, roller on the frizzen spring, and better engraving.
What is really interesting is comparing the GRF Hudson’s Bay Factor’s Pistol to the W & S Rooke pistol.
Obviously, the same trade pistol pattern.
You occasionally see an old CVA lock like the one above for sale on eBay, though the price can vary a lot. I think CVA discontinued importing the bridled lock decades ago, and replaced it with an unbridled lock like the Ryan & Watson lock. I’ve seen more of these unbridled CVA locks on eBay than the bridled.
You might look around to see if you can find an old CVA flintlock. If you can’t find one, then go with one of Chamber's late Ketland locks. If you keep the lock panels very narrow like on the original Ketland pistol shown above, it shouldn’t be too big for your pistol.
A .62 swamped smoothbore barrel from MBS would be a good choice for your Ketland trade pistol. My two round barrel trade pistols have barrels under 9 inches. It looks like the MBS barrel is 10" long. You could easily shorten it to 8¾” or 8⅞” long. Don't worry about cutting off the flare end of the swamped barrel. The barrels on my pistols are essentially a straight taper with little or no swamp.
