Welcome to G&G from Maryland. Years ago I was looking at double barrel black powder muzzle loaders but in 12 gauge. Not sure if you are looking for shotgun or a double rifle. These things were expensive then and really expensive now. Also limited to finding one as there are not a large supply of them.
Welcome to the Forum from the Peoples Democratic Republic of New York.
I agree with Bookman. Your best bet to find a double caplock rifle is one of the auction sites.
Edit: I just took a look at Gunbroker.com for double caplock rifles. They have a few Pedersoli rifles like the one jaydeencox sold and is now trying to replace, all in 5 figures. There are also a couple of antique double rifles, including one Atkinson-Remington superposed, that might do. Good luck!
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