Get a legal definition of well regulated militia, get it to not map to the national guard or some homebred terrorist group via some ritual like the pledge or whatever, and police the crap out of the gun sales to groups outside this definition.
By the Constitution's own legitimacy it's the government's choice to forego this control under those terms, and it musts be the government's choice to tighten this control up.
Why is it legal for me to own an elephant gun but illegal to strap it to a drone? For this exact reason: Definitions were established, and strapping guns to drones was deemed a dick move.
Same here, define legitimate civillian militias and take all the guns off the hands of every other random guy.
Couple years after that maybe we could start having the discussion of why you need armed death squads on your home turf but hey at least the ease of access for the general public is out, and with it a large part of the reason why the US os the only place where this happens day in and day out.