On the subject of backwards logic for dictatorships. They are probably the most likely candidate for having blackmarkets, yet the game does the opposite.
Think about communist governments and dictatorships today. Do they really allow the purchase of what you might call "battle weapons"? I would think they would be the MOST restrictive of weapons that could threaten their regimes, not the least. Lawless and anarchic systems is where I would expect things like battle weapons and nerve agents to be legal.
You might also add one more form of government: "Libertarian". That one might also see battle weapons legalized, although even they might get cold feet at the notion of letting nerve gas run loose.
Hey, what about nuclear weapons? Why can't I buy those in a high-tech anarchy?
Exactly. Governments don't control or stop blackmarkets, which is the point of a blackmarket. The more oppressive a government, the more likely there will be illegal trade.Black Markets generally pop up anywhere a legal market doesn't fulfill demand. Regardless of government.