At least on the Eastern Shore, a lot of private land is tied up in leases, especially when it comes to waterfowl. You might find a farmer who will let you shoot snow geese off his field, but even that is getting harder to come by.
I don't know of any central source for leases, but I see people advertise in the paper once in a while that they are looking. I'm not sure what kind of response you'll get, or the quality. (Unfortunately, when you do see a place that has "opened up", you have to wonder why. I talked to a guy once that was leasing a goose field where "the guys from last year got their limit every day." Only I happened to know "the guys from last year", and they didn't shoot squat!)
Best way is to make friends, get invited somewhere, show up with donuts or coffee, and just mention that you would be interested if they ever have an opening. Repeat as often as possible, then wait.