I don't specifically collect N. Korea, although I have an interest in South Korea so, like "Oldguy" I do sometimes acquire N.K. when buying a page of S.K.
When I worked in South Korea, I visited the border with N.K. and bought some items in the official N.K. shop, including some used/CTO stamps.
A few years later, when based in the U.A.E., I visited the Stamp Exhibition held in Dubai next to the Airport (2006?). The N.K. Philatelic Agency had a booth there, where I bought a 2002 Yearbook. Some interesting stamps, sheetlets and MS, together with some fairly propagandistic text.
It can be a little frustrating when searching for S.K. on the web to find sellers who can't, or don't bother to, differentiate between North and South when describing and listing Korean stamps. Of course
ebay rules and/or local policies may not allow them to do so!