Hi Shortbarrel,
Matchlocks, even snapping matchlocks are very simple devices. You can get castings for authentic copies from The Rifle Shoppe but in reality, you don't really need them. Anyone with rudimentary metal working skills can make the lock, even the snapping versions. Find books on the history of firearms by Claude Blair, Robert Held, Dudley Pope or even George Neuman' s "Battle Weapons of the Revolutionary War" to find drawings of the lock mechanisms sufficient to build one from scratch. Your biggest problem is finding an appropriately shaped barrel but even a big musket barrel from Getz and Colerain will do. Look at the books by the authors I mentioned for the shape of stocks and go for it. There may even be some good imagery on the internet.
dave