On Halloween, my grandma (I’m in the US) would dress like a witch and use dry ice carbonate homemade root beer she’d dole out to kids from a giant bubbling black cauldron. I thought grandma was an actual witch for a while there.
This kind of depends on the location/jurisdiction. The more rural you go, the more likely you can buy it. In a lot of big metro areas you'd be better advised to call ahead until you find a store that carries it.