Walk into any ACE Hardware, WalMart, Home Depot, or Sears, and you'll be able to grab (as in physically touch) a can of spray paint off the shelf, hand over a few bucks American, and drive home to spray to your hearts content.
No cages, no glass partitions, no workers clad in orange smocks suspiciously eyeing you as a potential lacquer larcenist.
No warning placard posted near the paint section about age limits. No signs citing the current fines/jail time imposed on convicted graffiti gangsters.
I imagine young pickup truck drivers around here don't yet have an interest in declaring their territorial borders in their "hood," nor do they find it necessary to let others know they were standing in that particular spot at one point in their youthful lives.
Although I did spot this example of local tagging on the railway overpass that is the eastern entrance into/out of my small town.