I am interested in using North Korean artists' work (mostly music) for commercial purposes. I cannot contact them so I don't know how to handle copyright issues. Even if there are such problems in this case. Are North Korean artists even protected by copyright laws internationally given the uneasy situation between the DPRK and the rest of the world?
Yes, North Koreans are protected by copyright law even though North Korea is not a signatory to the Berne Convention.
Assuming that you are in a country that is a signatory to the Berne Convention (which you probably are) the relevant consideration is the "Country of Origin". Only if the work was published in North Korea (or other non-signatory countries) and not published in a signatory country within 30 days is there no copyright protection - given that you have the music and presumably didn't go to North Korea to get it; it has been published in a signatory country and the author has copyright protection if this happened within 30 days of it being published in North Korea (which you have no way of determining).
The chances of a North Korean national being able to protect those rights is somewhat slim of course.
Without going into technical points at this time, you can give some credit to North Korean artists which will protect their moral rights, given the fact that you are willing to contact them.
Also I believe you won't be ripping down their entire work and will be creating your own piece of work, that'll give you some copyright too in your work and combined with some credit to korean artists, you 'll play safe & straight.