The owners of all realestate are listed with the county and are public record. Most counties have searchable online databases. If you live in a rural area though, you might have to go to the county seat/city hall etc.

For government owned property, most cities/counties have periodic auctions.

It is often harder than you might think to buy rundown lots or buildings. They are often abandoned for a reason - eg major site problems, huge back taxes, leans, judgements etc. Some cities have redevelopment projects that may assist potential owners, but that varies wildly by region.

Good answer. I had my eye of a very unique old house in town and was waiting for it to come up for some sort of auction or sale. Instead of actively pursuing it, I just kept my eyes peeled. Was hoping to buy it and save it from destruction. Never saw a condemned sign on it or any other notice. Drove by it one day and it was just 'gone' and an empty lot in its place. The city had come into some funding for derelict and abandoned houses and suspect they just solved their problem that way.