I believe there are a few "reputable" colleges offering Gunsmith courses. Personally I would not take one of the correspondence courses. An alternate method might be to talk to a few known gunsmiths in your area and offer free labor in trade for training. I am a retired Engineer that worked with (and designed and troubleshot) precision assembly testing equipment for about 40 years and do all my own "gunsmithing" within the limits of my equipment. Be aware that starting a real gunsmith business requires some pretty expensive equipment as well as the knowledge - a Lathe, Milling machine, (optional) Surface grinder, vice with adapters for all the type guns you intend to service - Hot blue tanks, spray equipment, etc. are all needed for a full service shop. This does not include the gages, bullet safe, license, spare part inventory, hand tools etc. Several of the Gunsmiths I have known start will a limited service type shop, specializing in certain type guns, and expand gradually as they can afford the equipment to become a full service shop.