If no one else finds it, you can go there and either carry it back with you legally (locked case, declared) on your next flight back. (A relative did the exact same thing here. Forgot it while he was visiting this state, and on his next trip, declared it when he flew back. No hassle.)
Or, you could take it to an FFL and pay him to ship it to a local FFL for you to pick up.
No need to go all wobbly over it!
I think that the point ALSO was that it is a prohibited item in the state of Kalerfornee...no legal means to return it.