I have done some searches for Gunsmith schools and can not seem to locate any. The AGI Professional Course is excellent and includes welding and machine work.(lathe and mill) It is about $10,000, but worth every penny. You can also do one of the other courses without the machine shop and welding or start with the Law Enforcement Armorers Course. The Law Enforcement Armorer one is around $800 and includes armorers courses on over 20 weapons and their clones.
A couple of searches suggested coming to the U.S. if you want to attend a school.