@Miriam

There are more differences than you think. North Koreans do not only learn the southern version of the language because of the accent which stigmatizes them, but as well because of communication problems. North Koreans usually do not know any English vocabularies, which have entered the language of the South (and they are growing day by day). North Koreans have as well more Chinese words in their language. There is even a generational gap among South Koreans, who do not know many English words which have become part of the South Korean language.

But North and South Korean are mutually intelligible. If I were you, I'd work with a South Korean teacher and South Korean resources until intermediate level and then compare the differences.

Edit: I just checked and in the language partner search, several North Koreans pop up, so you might try contacting those users directly for help.

For summary, refer to 
https://en.wikipedia.org/wiki/North_Korean_standard_language
https://en.wikipedia.org/wiki/North%E2%80%93South_differences_in_the_Korean_language

I don't believe you can find a North Korean teacher here.
If you want further information, try to contact North Korea University site which we could not access here in South Korea.

e.g.
http://www.ryongnamsan.edu.kp