Best thing to do would be to get some screenshots / high fidelity wireframes made for your application that you can just click through. Set this up in a full-screen browser on your iPad so you can click through it and demo what the purpose and goal of the application would be like.
Then just go to some local restaurants and ask to see a manager or owner. (ideally find this out before hand so you can ask for them by name) The person may try to stop you or inquire further about what you need to see the manager for and why.
Just tell them that you are a local mobile developer and you have a really cool idea for an application. You wanted to get some feedback from some real restaurateurs before you invest the time to create the product and that you only need 5 minutes of their time to get some feedback.
For the most part people are really accommodating with requests like this. You aren't looking to sell anything (today at least) and people genuinely like to help other people and also like to talk to people where their expertise or opinion counts.
When you do this get their name, phone and email address so you can come back and sell it to them once you create it :)
But definitely make something with a great user interface to demo. It doesn't have to actually be an app, and even click throughs of full page image designs is sufficient to get your product concept across.
Also make sure to run some financial numbers by them... "would you be willing to pay $30/mo for a product like this?" and get some feedback.