Russians are sitting on tons of them they cannot sell due to sanction. It is not hard to imagine that they will be glad to sell at a steep discount if anybody is willing to buy, which N. Koreans can exploit.
North Korea gets all of its fertilizer imports from China along with food imports to make up their shortfalls. Apparently Brazil, India and China (Russia’s BRICs economic group partners) aren’t completely in on any sanctions. Imported Russian fertilizer will be available to them, not the rest of the world. Ukrainian production is probably totally lost to the world. You are probably right China will be the facilitator between its old and new client states, the NORKS and the Russians.