A top notch gunsmith is a machinist first and a gun expert second. I doubt that you will be able to learn the trade from a CD or a DVD. You may learn the answers to the test that is required to get a license but you will have zero hands on knowledge. Your best course of action is to learn at the knee of a master, sweep the floors in the shop if that is what is required to learn the trade. There are no shortcuts to being a journeyman machinest or a master gunsmith.