If you're looking for a flinter that will meet AMM standards and don't want to spring for a custom gun or make your own from a kit, try one of the Brown Bess replicas on the market or an 1803 Harper's Ferry rifle or a Dixie Gun Works Tennessee Mountain Rifle. Dixie has the last two, Navy Arms markets a version of the 1803 Harper's Ferry rifle, and there are plenty of Brown Bess replicas out there. BTW The 1803 Harper's Ferry is the rifle carried by members of the Lewis & Clark Expedition. JJ Henry Trade Rifles are correct for the era but as far as I know there are no factory-produced copies available and customs are pricey ... upwards of $1,000 each, probably. Leman Trade Rifles are the same way. You can see a good many original Fur Trade Era rifles and smoothbores at the Museum Of The Fur Trade site, and the Museum Of The Mountain Men site. A company in Nevada called "JJ Henry Artificiers" makes excellent copies of the Henry Trade Rifles and they also have a website.
There floats my stick,
Tanglefoot