DOJ's stolen gun file does exist though, so the dealer was negligent in not checking. It may not be worth it for you to sue, but that means you'd win. Since the dealer failed to check the database, he's open to prosecution for dealing in stolen merchandise and unlawful firearm transactions. Any criminal case here may be weak, but not a civil case.
I'm glad I posted this for all you FReepers to give input. Frankly I don't know what to do at this point, but it certainly is educational.