There are several ways the first is the quickest, would be to go online to google and to do a search for stolen guns list. You can also use wiki answers on the world wide web. There is also the National Crime Information Center which can be accessed on line or by going to your local lawenforcement agency.
The NCIC (National Crime Information Center) tracks all guns that are reported stolen. If you have a gun that was stolen, first contact your local police. Once the police have this information they can contact the NCIC who will add your gun to the list. If and when it is found, you will be contacted.
The only way to find out about if a gun is stolen or not is to check with a police station. If the gun is stolen then they will get the information about where you got the gun take the gun from you.