The outside consultants, if they exist, who can fit your profile best, are Chinese. Most of things N. Koreans need to make a rocket pass through Sino-N. Korean border one way or another. They could be components or industrial equipment for building a rocket. People tend to talk about Stuxnet type of malware planted by the West which can disrupt their rocket performance. Chinese are far better positioned to pull such a mischief. They can plant bugs and malware on everything if they want.
That does not mean that they actually did it. They might as well have sold faulty components to N. Koreans at a huge markup. However, if they want, they certainly can.