There was a college in Quebec that was doing a gunsmithing course. Dunno if it's French only, or if they work in English too. I would think that they wold be similarly having fewer positions than applicants. But maybe not.
As for the home-study diploma, I'd suggest that you would be money ahead downloading a template and printing your own.
Take some small business related courses on bookkeeping and the like. I have met a fair few gunsmiths over the years that were pretty decent mechanics, but lousy at running a business.
Cheers
Trev