Just a quick note about bags. I see many folks today with fine rifles, beautiful horns, but bags that look like they were made from roadkill. Like in the "mountain man" days in the 1970s, some people tended to follow like sheep and there were a lot of raw looking buckskin bags with long fringe. Likewise today we see many people buying primitive bags that look like they were done by someone living in a cave with no resources. If someone could afford a nice rifle, they could afford a nice bag. Think that through before deciding on a bag.
Since Young was from Easton, PA, a primitive Appalachian bag would not be appropriate.
My suggestion would also be to go with a fairly plain bag. If you pick plain, you won't likely be called out as "historically incorrect" in time or place.
For horns there are many good makers, but Tim Crosby mentioned here and Ron Hess would be good to contact. I have several from each, and they are all delightful. Keep in mind you'd most likely want a PA style horn.
For bags Darrel Lang and Lawrence Fiorillo would be good to investigate. They both make fine bags. At the top of the heap is James Rogers. His bags are works of art, but he may have a waiting list now.
I hope this helps. God Bless, Marc