The most common historical solution has been backyard and community gardens. They were common after the soviet collapse, and during WWII in North America.

I know you said “and not wait a growing season” but some backyard crops can grow in 21-30 days. And masks took longer than that. There’s a lot of yardspace that could become gardens and chicken farms in a pinch.

A big risk would be if that happened during the winter, or in a place where there is less surplus fertile land.

If there’s some event where you can’t grow, the only current thing we can do is already having non perishables stockpiled. We didn’t event a whole new supply chain for masks: existing companies ramped up production and citizens/new companies made cloth masks. But we’re talking established techniques.