Are there currently efforts to hunt down (for example) Big Vern, and the guy (Danny?) from Neo and Bee?
Just asking...
What is the "proper" Libertarian view on dark markets that offer bounty hunters/ vigilante justice?
You would need a way to be certain the person is guilty, before subjecting them to a "free market" justice system.
Any thoughts on how those would work in a free society? and/or do they actually exist now?
If you were certain the person was guilty then that should be good enough for typical through-the-court-system justice, wouldn't you think? Siccing a hired hitman on a scammer doesn't depend on justice, it depends on how much money you have.
And yes they're available, but I would have no idea who to contact specifically. And I'm not sure if there's any effort to track down the Cryptsy scammers. There was a thread about a lawsuit but I haven't been following it.