I'd hop in, or on, my favorite mode of transportation & go for a ride & see who else has large veggie gardens in my area....surely some will be visible from the street/road. Then I'd go knock on their door, and after a heaping helping of praise & admiration for their beautiful garden, kindly ask who plowed all that dirt. If they did it themselves, but aren't willing or able to help you with yours, they may very well know someone who can.

or, like you said...check with local feed stores, farmers co-ops etc.

you might even try a small ad in the local paper...

good luck!!