My experience in things like this, is that it's the promoter (whomever rented the facility for a concert, race, event, or whatever) is responsible for turning it back over to the city, county, state, or whomever, in the same condition as they got it in.
But of course, that's not to say that the owner of the facility might not also need sweeper service in the course of general maintenance. So for example, if they are about to rent the stadium, or park, or blocks-of-city-street, or whatever it is to some entity, the entity can say "there's grit and gravel, it's not clean", and thus the owner might sometimes call a sweeper to do a pre-cleanup. In that case, it's the owner who's doing it. Naturally, they will expect it to be just-as-clean when the event is over, as a condition of contract
So you should find out who does these concerts, flea markets, street faires, festivals, races, or whatever it is going on, and find a way to market to them.