MikeB4: It may not necessarily be Russia and China supplying directly. An example, Israel purchasing and being supplied Dehavilland Mosquitos posing as the New Zealand Airforce
I suspect that a main problem for NK would be a cashflow issue - they don't have a buoyant economy,
Don't think it'd be a major issue putting together a deal through a Chinese trader - in this case the (NZ) supplier probably had no idea what was going on.
Fighter jets and other armaments - perhaps not. OTOH they seem to be doing okay in their DIY fashion But they will be needing to import materials and components. They even have a DIY satellite in orbit.