Regardless of how you get your gun back, I hope that you will, and that you will still find a way to take it out on his behind.
That is ridiculous! And you shouldn't have to defend yourself about the value of that gun - although I did laugh about the reference to the Kate Spade bag
Let us know what happens after tomorrow when he will obviously show up without your gun.
I think that the Uncle will be more than willing to give your gun back. He should get his money back from the guy - not you. Especially after you can prove that the guy had no right to sell it. Like I said - I'm sure the Uncle will be reasonable. Keep us posted.