In general, I agree with you that the way English-speaking countries have let their tradition of citizen-soldiering die on the vine is a terrible thing. There’s no reason that the vast majority of high school graduates couldn’t have the basic knowledge acquired in Basic Training by the time they graduate from high school, if with somewhat less discipline and rigor along the way. There is an army of retired/mustered out NCOs who could lead such things part-time, much in the way thing like sports coaching are done.
IMHO, this would be a far better use of our Defense budget than shoveling it to the Beltway Bandits on ephemeral shiny toys.
There are many latent structures in our laws that could provide for this, it just remains for some men to take advantage of them. My own state approved an increase in the upper age limit of the unorganized militia a few years back. The practical implications of this are nil at the moment, but like I said, the laws are still there.
There was a movement building in Virginia to start forming militias under the authority of county sheriffs. This was in the wake of the big gun control push there. I suspect that it may have gotten lost in the Covid shuffle, but it doesn’t appear that the Virginia Democrats’ appetite for gun control has been blunted any, so that movement may resume momentum at some point.