During the current shortages, the least popular stuff has been available all along. ,308 has been on the shelves around here when nothing else was. Same with .44 mag handgun ammo.
I always thought that if I had the most common calibers, I would always be able to get ammo, now I think perhaps its the less common stuff, stuff that there is not so much demand for, that will be available if things go south.
Regardless, I am not likely to survive to see the end of my ammo supply, so I don't really worry about it.