Richard: Most gunbuilders today use parts manufacturered by other commercial suppliers. Finding parts for the gun after the gunmaker dies is not as difficult today as it might be with a 18th or 19th century original build. I do think its smart to buy extra main and frizzen springs, an extra frizzen, maybe an extra tumbler for a lock and hold onto them " just in case". If you have a truly custom made gun, from hand made parts, and you didn't think to ask the maker to provide you with extra springs, etc. you might have to find one of the rare gunsmiths who actually knows how to make springs. The trick is to remember to ask him to make you a couple of extras of whatever he does make for you. The labor costs are going to be the big cost, and once he makes one part to correct size, it takes much less time to make another.
MY problem with buying guns made in Europe is that its next to impossible to get parts from the company, and, of course, its not helping the American economy to be sending our dollars overseas.
I encourage friends to "Buy American", whenever they can. I make that a personal habit with everything I buy. Sometimes, I am left with no choice, and when that happens, I let the store managers know my displeasure. They may think I am just some old Curmudgeon, but at least they know oone customer is not happy with the fact that they stock only good imported from China, or India, or someplace else. Overseas gunmakers don't pay the Pittman Robertson Excise taxes that are imposed on Domestic Gun manufacturers, making American companies less able to compete, and screwing up our balance of payments overseas.