Iran was there all along. I know; I was being sarcastic. Oil is a source of cash flow and the Norks don't have much else to sell. I seem to remember the Chinese supplying the Norks precursors too.
Since 2002, the United States has sanctioned Chinese companies for providing North Korea with tributyl phosphate, an acid solvent used in the extraction of uranium and plutonium salts from nuclear reactor effluents. (Source: Bill Gertz, "N. Korea seeks aid from China on nukes"; The Washington Times, December 9, 2002, page A-01) All one big happy family.