Three million rounds sounds like a lot of ammo, and I wouldn't want to carry that much very far, but it is small potatoes to an ammunition manufacturer. I wish everyone who owns one of those old Winchesters a lot of luck in finding ammo or getting new production started. The problem is there is just not enough demand and no company wants to stick its neck out to make a bunch of something it can't sell.
BTW, .22 WMR is an elongated .22 WRF so firing .22 WRF in a .22 WMR chamber is like shooting .22 Short in a .22 LR chamber.
FWIW, the reason for the .22 Winchester Auto and the .22 Remington Auto was that when the guns came out, the .22 LR had not been fully developed; loadings were not uniform and .22 LR was still loaded with black powder. Not only would black powder gum up the works of the new rifles, but its pressure curve resulted in poor functioning.
So, in order to minimize problems with the new autoloaders, both companies developed special cartridges which they would load and control; the cartridges, the .22 Winchester Auto and the .22 Remington Auto are similar, but not fully interchangeable.