Occasionally when stories about acid attacks reach lesser online forums, the comments will indeed be filled with cries of "why the hell are they even selling acid?". The commenters presumably do not realize that their local hardware store just a few minutes away is selling nasty shit as well.
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.
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.