What about the 1964 Silver Dollars they minted in Denver and then melted? Allegedly they melted all of them but several are rumored to have escaped.
If you come up with one of these it will most certainly be seized.
Reminds me of the story about the poor Irish widow wrote to her IRA son in prison"son I don't know how I'm going to spade up the back garden,me with a bad back and all"So the son writes back"Ma,for G-- sakes ,that where the stuff is hidden" Next week the widow writes"Son,some nice men from the police came over and spaded up the whole garden ,bigger and deeper than you poor da' ever did;wouldn't let me help at all!"