I may have found what you are looking for. You might want to turn the other cheek… in photos anyways.
The Lyman cap & ball Trade Rifle & Plaines Rifles are very similar to the one you have.
Link to Lyman Trade Rifle parts:
The spiral finial on the trigger guard is very distinctive. I only saw a single example except on the Lyman kits.
Lyman sells muzzle loader rifle kits. The hand grip part of the trigger guard is the same shape as that on your piece. It also has the sliding dovetail barrels for the ramrod.
The model that most fits is the "Trade Rifle." It has a single locking wedge on the 1/2 stock without a metal cap on the hand grip.
It has a single trigger, unlike the "Plaines Rifle" I used as an example. It simply had the best image quality that I found.
It could be that Lyman used the trigger guard detail & single fore stock pin because it was how trade guns were made. In any case, I did not see a single example of it anywhere else.
Link:
Musket evokes spiritual side of hunting.
www.canadashistory.ca
The Lyman Trade Rifles are of high quality. The reviews are consistently excellent. An Italian company makes them.
Conclusion: There are some differences between the Lyman & trade gun pattern rifle in the photos. At least it puts you onto a possible source for parts.
Lyman made the Trade Rifle in .54 caliber, which is unusual. That is a potential source for a period correct ram rod. The sliding dovetail rammer guides may not be a perfect fit, but should be no trouble to adjust to fit. Same with the front sight. Obviously you don't want to start filing away on your piece. However, a gunsmith could easily make the Lyman parts fit.
Good luck, post photos when you restore your family relic.
Northwest Trade Guns
This image shows the same proof marks as your piece on an English Northwest Trade Gun. It is from the article liked. If you look close, it looks a lot like the same spiral trigger guard finial as yours.
Link:
Does anyone know about how to find a date range for these English proof marks from the barrel of this smooth bore gun? Any help would sure be appreciated!
www.muzzleloadingforum.com
Northwest Trade Guns had a very distinctive what we would call a logo. This distinctive dragon plate was a fixture of flintlocks until 1877; cap & ball rifles until the end of the Century. It was not always this elaborate. Other examples
I knew almost nothing about Northwest Trade Guns before starting this search. The Longhunters that came over the mountains into Tennessee have been a long time interest. This was something new & the dragon plates are really something. The link is to the article where these images came from.
Link:
https://www.speakingcedar.com/in-depth-
northwest-guns.html
Link:
Percussion 54 Caliber Rifle, back Action, Barrel Marked "F. Hellinghaus St Louis" Half Stock length Stock. Lock Not Marked. Frederick Hellinghaus was active in St. Louis from 1840-1847. After moving from Baltimore Maryland. He eventually settled in San Francisco, Ca Circa: Mid 19th Century Size...
kentantiquegallery.com