Two things come to mind. First, When you're at a restaurant and you notice that they need your services, point it out to them and give them a card. Talk to the manager of course, the waitress could care less. Second is that there is one type of business that caters to all restaurants, and that's the restaurant supply shops. Maybe they have a board or something that you could post a flyer or business cards on. Oh, wait, I guess there are two places that cater to restaurants, the other being the ones that supply them with food.
If you really want to get aggressive on the advertising, either one of these businesses might sell you an address list of their customers that you could use to send targeted advertising.
If you really want to get aggressive on the advertising, either one of these businesses might sell you an address list of their customers that you could use to send targeted advertising.