I'd suggest polishing your in-person pitch and hitting venues where food trucks gather. These events happen weekly in major US cities. You should go one week to observe the customer lining up patterns and then pick an appropriate time the next week (maybe when the food trucks are wrapping up for the day) to approach the food trucks with your pitch.

Here's just one example of what I mean
http://offthegridsf.com/markets/fort-mason-center