[_delirium]

If it happened enough I could imagine there being some kind of controls. Bulk purchases of certain kinds of fertilizer were controlled post-Oklahoma-City, for example. On a lower level, some jurisdictions have restrictions on spraypaint sales, in an effort to combat graffiti.

[monochromatic]

There are all kinds of caustic chemical that can be bought in small quantities though. We're not talking about needing a truckload of the stuff to do something horrific.

[pyre]

E.g. in Portland, Oregon you have to show ID to buy spray paint.