I'm sure ice cream trucks use dry ice
But I'm not sure they're just going to let you have some (it's not exactly a secret what you can do with it)... unless you ask nicely and say you need it for a picnic or something, although that wont work atm as it's coming into winter. Other than that it's pretty hard to get hold of some unless you are a school or company ordering it for a valid reason other than using it for bombs.