If the firearm manufacturers, the firearm dealers, and the NRA all got together and came up with a voluntary industry standard for training requirements, I think I could get behind that.
For example, let's say the NRA came up with a couple of different classes, one for handguns, one for hunting long guns, one for self defense long guns. When you complete a course you get an NRA card.
A retailer who is participating in the program will require you to show the card before they will sell you a firearm. And of course, participation in the program is volutary, but it would come with benefits. I could imagine that some gun companies might require that all their dealers participate.
I could see how a industry-led program could have some real benefits. It could reduce the number of firearm accidents. It could generate good-will among the non-firearm-owning public. A lot of industries govern themselves with industry-led standards organizations, requirements, training programs, etc. SAAMI is one such example.
I would be opposed to any government mandates or requirements. Bad idea, and not in keeping with the 2nd ammendment.