Really?
FFL requires $300.00 and a government background check... Contact BATF (sometimes in phone book, if not FBI can direct you), they have a packet. You do not need any correspondence school for that. -!!-
"Certification?" Really. By whom for what about ??? I am sure they will sell you a nice piece of paper for your money. Worth it? I doubt... Friend of mine took one. He got all excited to learn that Browning had licensed the A-5 to be made in USA and now the USA model was cheap, cheap, cheap... Great history info, not much about working on guns... USA model? Remington model 11. Savage made a copy too. Model 750 I think. Remington could use Belgium parts WITH FITTING. Savage was not that close.
Basically, the gunsmith is a machinist, a wood worker and a small business person. You probably have a local community college with courses on all three AND help finding work in these fields while you get your business up and running. [Or decide to do something else.] You need some manual dexterity/ fine motor skills. I wanted too. My "fine motor skills" said NO. Luck.