Guys, I am interested in learning to become a gunsmith. There is a good one in my area which is heavily into hunting of all types, and he is getting ready to retire. There is enough market that I could potentially do very well. Now, I have bedded my own rifle, assembled my own AR's including rebarreling, and am very mechanically inclined. I did have machine shop classes in high school and did well with the lathe, etc.
How do I go about getting truly qualified to repair firearms? Schools? Correspondence courses? Machining classes?

Start with the manufacturers,most of them give armorers courses.

You're already in Kansas, Dorothy.

Intead of re-inventing the wheel, I would go that gunsmith (assuming you respect his work and HIM, and talk to him about apprenticing to take over his business.
You may be surprised at how he reacts...either good or bad.  There is nothing like a good relationship to quicken the learning process, and no book wil ever take the place of a master at your side.

Try here, they are supposed to be pretty good.

www.schooloftrades.com/GUNSMITHING/ABOUT/INDEX.CFM

First, go on a strict diet and figure on staying skinny.

That's because there's little money in it.  There are two types of gunsmiths:  general gunsmiths who can do real stocking, action work, etc.  They're good with machines and hand tools.  They're starving because Americans want to buy a disposable rifle like a 10-22 and hand it down to their kids.  

There's another type:  the custom guys who specialize on one or two types of arms.  .45 smiths are like this.  They can make a good income by running a customizing factory line and pumping out a lot of guns.  These guys run from truely skilled guys to garage assemblers.  The AR market is full of the assemblers.

Few smiths really develop the production levels and reputation to make a good living.  It takes a pretty good chunk of money to get started properly.

two hundred years ago firearms required a lot of repairs because of the materials used.  Gunsmiths were common.  Modern materials make firarms very durable and handwork isn't needed.  Gunsmithing by parts replacement doesn't pay much.