Sure their is. There's a whole system dedicated to it. You make a brochure describing the service you want to offer to the restaurants. There are then companies that will print as many copies of that brochure as you ask them to, put them in envelopes, and mail them to addresses on a list you provide. (There are companies that will make the list for you, too).
Combine that with phone calls to the restaurants you think would be most beneficial to get on your service. Three salespeople using phones could contact 10% of the restaurants in Los Angeles in under a month, and all of them within a year.
Restaurant delivery is local. You don't have to compete with the incumbents nationwide right from the start. You can do it one city at a time.
DoorDash, for example, started in San Francisco with something like 75 restaurants. That feels doable even with this bill. Today DoorDash is worth something like $15 billion. If you actually have a better idea and can execute, you will find investors.