The military puts a date on everything and gets rid of it after that. It’s for safety reasons and maybe also to line the pockets of someone in fedgov most likely. That 3M 8120 model is listed on 3M’s coronavirus page too as being a decent one for us peons. Those might be the only ones left in the country.
If you know anyone who can buy direct from the military, now might be a time to look them up. All kinds of stuff comes up for sale. Can turn a decent profit quick on the flip. Know someone who purchased direct for his spec op troops. Still kept the buying capability after leaving and uses it on the direct military surplus sites.