You can always keep a few to turn in in good faith and for the rest, say you sold/traded/gave them away. Copy of the classified ad you took out (you told all callers they were already sold) a handwritten receipt with drivers license # (how were you to know it was fake?) may be just enough to let you live. Probably not a good idea to report anything stolen though. If you ever give it to your grandson and he gets stopped for a traffic ticket, you don't want him to be in possession of a "stolen gun".
So, it would not be a good idea to say they were stolen "a week from next Tuesday" ???