Just check the newspaper, they often get listed every week. Easy way to see them as they pop up.
Else, access your state MLS system. If you're lucky, there's an interface for normal people to browse listings and obtain contact information for agents. There are a few telltale signs to look for, starting with the ownership. If it's a bank or some other institution, that's a red flag. If the price is below assessed value (your city/town should have some way to search property records appraisals) by a signifcant amount, that's a red flag too.
There are ways to find the information using what's publically available. These subscription services just pay MLS and other organizations a small sum to have the database access. Or, they just dig through the databases and compile the information themselves. It's like police record searches. This is a waste of money if you know a) the person involved b) the docket or arrest report number c) the telephone number for the police department in that area or the court clerk.
It's called footwork.