Well, at least we're not invoking prima nocta, to get a gun back.
Outside of LE resources, you're probably up a creek. This is going to sound insane, and tedious, and about as productive as banging your head against a brick wall- but for a family heirloom, it could be worth the trouble. Start burning up the phone lines, call every pawn shop, gun shop, museum, antique house or auction house whose number you can find. Start in Spruce Pine, expand it to all of NC, the southeast, etc. Ask them if they have any Toks. Tell them your story. Tell them the serial number. You never know what might materialize, and it can't hurt to have more eyes/ears tuned to the situation.
I know that must sound like an awful idea. And unfortunately, after thirty years of being in the wrong hands, the fruits of your dad's sacrifices probably ended up in a sewer, or melted down, or in the Ukraine. But I wish you luck, sincerely. I hate hearing stories like this.
Proverb for Paranoids: The innocence of the Creatures is in inverse proportion to the immorality of the Master. -T. Pynchon