North korea has some rich copper deposits iirc. That is why one of their exports is large bronze statues of dictators (no joke) and presumably the capability to make casings. They also have hydroelectric power despite the population not having access to this, using this to manufacture explosives and other armaments would make sense, that is what some european countries did too in the past. They also have a devision that produces biological and chemical agents. What those exactly are is not known (or at least not disclosed by those that do) but all soldiers that defected are still vaccinated against smallpox and nerve agents are pretty easy to make. So we can make some guesses.

They also produce tanks and submarines but I doubt they will be a match for anything produced recently. Although north korea does have guided missiles, but maybe still relying on soviet tech? Or not who knows.