Here's a google drive I found full of documents, biographies, reports, counterprop and theory for Juche, Songon and just about everything else DPRK:
https://drive.google.com/folderview?id=0B48PXBn7S_-MMVlaZjlrOEdKWFkThere is notably some very recent documents from as late as last year, including the theoretical work of Kim Jong Un.
Everything (I have seen) in here is in English.
(If you are (rightly) wary of Google here, know that you can view and download these files through a Tor browser.)
Anyone got anything else DPRK-related they don't see here that they'd like to archive?