Odds of Getting In
The odds of getting in are pretty good; there's not a lot of competition out there for this career. It may, however, be difficult to find a class near you.
If there's nothing in your area, you may be stuck going the formal route, studying somewhere like the American College of Building Arts and majoring in forged architectural ironwork. Other majors at art colleges to consider include art metals, welding technology, blacksmithing, and collage.
Okay, so the collage degree won't actually help you become a great blacksmith, but you'll probably bring home a lot of cool stuff.
Long story short, blacksmiths who know how to blacksmith and have somewhat reliable access to a forge and materials are already blacksmiths. There's not a lot of "getting in" from there.