I write this as an elderly person who have lived muzzleloading since the early 70's. I started early in making "scratch" muzzleloaders meaning rough cast metal parts, a rifled barrel and a blank. Over that time I found cast parts harder to find and the quality of blank wood has gone down with cost going thru the ceiling. All this said, if the demand is there, someone will take up the manufacturing of those part. So, is there going to be craftsmen making custom ML'ers? A few of the best, but if you are a modern gun maker you really need to be machinist. If you are a muzzleloader maker all you need is some carving tools, hack saw, sandpaper, etc. and when you get done just maybe it will be worth the parts you put into it, but the sense of ratification of completing something of beauty is there. My point is this: There are so many kit and part muzzleloader builders out there, my perspective is the money for a craftsmen will be few and far between. Those are the ones which will hold or increase in valve and not much at that.
If you want a custom muzzleloader build it from a kit or scratch. Some kits do almost everything for you. Decorate it up by engraving, carving the stock, checkering it, brass wire inlays, or what ever, and sign it. Give it to a member of the family who has posterity who may enjoy it. That is after you are done with it. Or just buy a custom gun, which will doubtful be a good investment. Write up a history of times with that gun with your thoughts. With the internet you can learn to do anything nowdays.
I made a lot of scratch guns of which went to family members. They were made with the best parts I could purchase and the best curly maple blanks. The parts for the first guns cost around $300.00. Maybe those guns would fetch double the parts costs, but now to make those same guns the parts are nearing $1000.00 to build and just maybe the gun would fetch $900.00. That is conjecture at this point. Some of these custom or kit guns are like purchasing a new car. Shoot it or drive it off the showroom floor and it's worth half what you paid for it. That is my thoughts on it anyway. I'm sure others have differing opinions.