Guys, guys, guys. The only cartridge you need to protect yourself from the virus is a P100 cartridge, or HEPA. You don't need to buy a CBRN cartridge which costs between 80$ to 240$ ea. It's ridiculous.
Most military masks, like our C4 (wink wink), use 40mm NATO threaded cartridges. Some PAPR cartridges which are not sold for military/defense purposes fit the bill. More specifically, one example is the North 40HE cartridge, usually found in packs of 3. They're not advertised as 40mm NATO, but I validated this info with Honeywell Safety and tried it on my mask. Perfect fit.