The problem with buying from a realtor is that often times they will ignore any property which won't bring them in a ton of money. This means most vacant and run-down country land. The only time such land is listed, it is usually in bulk, or because a bank is asking the realtor to sell it for a higher price. So instead of searching online, I figure that it is superior to look for run-down, abandoned land, with no realtor signs, and then ask a neighbor who owned the property. They will be able to give a name. If not, check with another neighbor. Take this name to the county public land records. Once you find a listing, check it out. Call the county sheriff's office and ask if it is still for sale (sheriff's office normally handle auctions). If he land was up for auction, and the auction has passed, ask if you can purchase the property. With any luck, they will be willing to sell it to you, and a low price at that. They want more tax slaves after all. Also, you can use google streetview in many places to explore remotely.
This method worked out for this guy:
The only change is that he took out a loan, which may not be needed if you can get owner financing for the property (given that you aren't going to build/renovate a "traditional" house)