Well, I'm sure Iran or N. Korea could sell a nuke, could they be untraceble doing it?
What would the response be to a terrorist using a nuke from Iran in the US?
I imagine a whole lot of tactical nuclear weapons used to put Iran in the stoneage for a long time... Plus anything that even looked like a munitions factory, let alone a nuclear facility would be destroyed as they built the forms for the foundation for years to come... I'd think the leaders of Iran would come to the same conclusion, and riding around on horseback makes it tough to spread their ideology.
If N. Korea got caught selling nukes it would be a bit stickier, what would China do if the US did air strikes in N. Korea? I don't know, probably nothing but things wouldn't be friendly...
I think Iran will never have nuclear weapons as long as Isreal is backed up by the US anyways.