You have a regulatory authority step in, and allocate the masks to people who need them (e.g. healthcare workers). Sales from individuals are banned, and said a

You have a regulatory authority step in, and allocate the masks to people who need them (e.g. healthcare workers). Sales from individuals are banned, and said authority can buy them back from people who own them. Just like how the government buys back land or property if there is important construction that is to be built over it, a similar procedure can take place here.