LawrenceN....Don't read more into this than actually exists.
"Old Time Gunsmiths" did do excellent work, as so many surviving specimens from that era can attest to.
However, most gunsmiths, even back then, did not make all of their own parts as many were readily available on the market.
Barrels blanks, or barrel scalps of bar iron for forging gun barrels, were available as early as the 1830's.
Many early Gunsmiths rifled their own barrels from a "blank scalp", or barrel blank, with a pitch that they felt was just right for the projectile which the gun was designed to fire, be it round ball or conical, and a select few even cut their own barrels in whole from these "scalps", but for the most part the barrel was ordered then rifled.
Most of them did 'refine" many of the parts that they had bought on the market, some by simply polishing the workings of the lock and trigger, and then adding their own engraving to both the locks, and the side plates.
Most of them did do, or would do, the stocks to a buyers specifications to include length of pull, cast-on, or cast-off, and height of stock comb to the sights of the barrel.
As far as them having "off-the-shelf" replacement parts for potential buyers, I am not sure that existed. Certainly not as we know "off the shelf" today.
The replacement of parts, "custom" fitted to a particular rifle, or repair in general, has always been the real "Bread & Butter" of most Gunsmith's income, because that is where his skills truly shined.
Custom rifles, such as the one you're the proud owner of, would have cost more than the average workers annual wage, likely even twice the annual wage, back in the year that gun was made....consequently, there were not very many made, and those owning such rifles took the best of care to insure, not only their accuracy, but their longevity.
Think of it like this....if a Hawken, from the Hawken Shop in St. Louis, MO cost the average hunter of the fur trade era the equivalent of a years wages, one can only imaging what a rifle, such as yours, would have cost 'back in the day'....and even back then, Sam Hawken did order a lot the "parts" that after fitting made the Hawken the gun it was recognized as being during that time frame.
There is a familiar saying that goes like this: "A lock is a lock and a trigger is a trigger" no matter what modification is made to change, or perfect them in some way....their function remains the same.
Adding to that the old saying of "Lock, Stock, and Barrel", it is very easy to see we're missing one key ingredient, and that's the trigger.
Hope this helps you a bit.
Sorry I got long winded, but some subjects just need a little more 'talkin' than others.
Russ...