Lonesome, you don't have too many choices. For factory guns, search Traditions and Pedersoli flintlock pistols. They have several models, but as
Loyalist Dave points out, each would be a compromise for what you want.
To get something to better pair with your trade gun and trade rifle, you will have to look at custom pistols. Even there, suitable parts are hard to find.
Back in the 1970's, you had the choice of GRRW's Trapper Pistol in flint or percussion.
Thanks, My trade gun is a Green River Forge and I would love to find one of his pistols but you are right they are few and far between. I have looked at the suppliers..not much of what I am looking for. Not into building a kit. I will just keep my eyes open and see what might come along.
Thanks again.
LC
Or the Hudson Bay Factor's Pistol from Green River Forge. The Hudson Bay Factor's Pistol was pretty close to many original English pistols. Original on top and GRF Factor's Pistol on bottom.
Unfortunately, Green River Rifle Works and Green River Forge pistols are difficult to come by today, and therefore are expensive.
If you go the custom build direction, you could copy one of the pistols above. These would satisfy your .54 caliber need.
For a pistol to pair with your NW trade gun in 20 gauge, you might consider one of the pattern below. These were inexpensive English trade pistols that were imported into America by the thousands. They were used as horse and coach pistols back east and probably sold in hardware stores throughout the country. The Hudson Bay Co. and the North West Company ordered them for their trade, and they likely made their way to the rendezvous in the Rocky Mountains. The basic pattern changed little from the mid-18th century to the mid-19th century. The style of lock and the makers were the primary changes to the pattern over time. They all had round, smooth bore barrels and most were equivalent to modern 20 gauge.
This one is a Ketland from the late-1780s or the 1790s.
This one was made by Sharpe and probably dates to the 1820s.
Muzzleloaders Builder's Supply recently started offering a suitable trigger guard and butt cap for replicating one of these trade pistols.
https://www.muzzleloaderbuilderssup...gi?cart_id=5537351.31185&p_id=TGP-KET-B&xm=on
https://www.muzzleloaderbuilderssup...cgi?cart_id=5537351.31185&p_id=BC-KET-B&xm=on
They also offer round pistol barrels. Since these pistols were English, you should use a lock with a round pan such as the L&R Model 1700, Manton flintlock (Track calls it the John Bailes flintlock).