Solution, be honest: "Masks work, but we don't have enough and need them for hospitals so you're not allowed to buy any. Wrap a tshirt around your face instead, it's probably better than nothing."
Imagine if instead of putting out a press release, they had quietly banned selling masks by retailers and then 3 days later when people caught wind of it explained the shortage mean they were only for hospital workers.
All the anti government reactionaries that are now anti-maskers would be the most ardent mask wearers.