That's a nice idea, a good idea. Valentine's Day sounds nice, but it might be nice to add other holidays. Perhaps a restaurant could have a monthly or quarterly event for people like us. I can see some benefits to an event like that, although I wonder if enough people would attend to make it worthwhile for the restaurant.
After my Dad died, my Mom joined a group called Parents Without Partners. The name clearly defines the group's focus, and I know that the ability to socialize with people in similar situations was helpful for her. Instead of a restaurant hosting such a gathering, perhaps an outside group could put together such an event, and reserve a space for the attendees at a nice restaurant.
Similarly, the folks in my apartment building get together for lunch now and then. We choose a restaurant, folks sign up, we reserve seating, and people who'd not usually socialize get together and enjoy a meal and one another's company.