The Mid-Atlantic Gardening Forum does one twice a year and I think thy run well. Check out the "Exchange" part of that forum for their "rules." The MAG swap I went to was set up in a field behind a GardenWebber's house and the cars just parked side by side and people set their stuff out the back. If you're in NoVA, you might want to come (it's in Maryland)!

Thanks, Leslie...I have a very large yard and I'm planning on everyone parking by the roadside and setting up on the lawn closest to the road...thanks for the info.
Margaret