Thus, the new Kh-35s are a significant upgrade to North Korea's anti-ship capabilities. It's notable that Pyongyang displayed them at a time when the two Koreas' navies and coast guards have been exchanging fire across the NLL on a fairly frequent basis. This suggests that North Korea has probably had the Kh-35 missiles for some time, and has decided to display them now to send a warning to Seoul.Regardless of the exact timing of North Korea's procurement of the missiles, the obvious question is which country sold them to North Korea? One possibility, of course, is that Russia sold the Kh-35 directly to Pyongyang. Indeed, Russia has exported the Kh-35 to a number of different countries, including India, Algeria, and Vietnam.
However the fact that Russia has exported the Kh-35 missiles to numerous countries makes it harder to pinpoint North Korea's supplier. North Korea's most likely source is Myanmar. As The Diplomat has previously reported, Myanmar's Aung Zeya class frigate are equipped with Kh-35 anti-ship missiles. Myanmar's air force is also believed to have an air-launched version of the Kh-35 missiles. Although Russia doesn't appear to have acknowledged theses sales, Myanmar's Kh-35s almost certainly came from Moscow. It's possible but less likely that Myanmar procured them from another countries that imported them from Russia, such as India or Vietnam.
Myanmar and North Korea have a long history of military cooperation, which includes both countries selling the other side defense technology and weaponry. By contrast, while the Soviet Union certainly provided weapons to North Korea during the Cold War, there's less evidence that it continues to do so today in any significant manner.
Given that the Kh-35 missiles weren't completed until after the Soviet Union's collapse, this leaves Myanmar as the most likely source for North Korea's new anti-ship missiles. If so, the exact timing of the exchange becomes important because — although Myanmar has long sold North Korea weapons — it has assured the U.S. in recent years that it has severed all military ties to North Korea and is abiding by the UN Security Council resolutions against North Korea. There has been considerable evidence to suggest that this is not entirely truthful. Still, selling North Korea the Kh-35s after those assurances have been given would be a particularly egregious provocation.