Let’s clarify a point here: Silk is not and never was exclusive to China. As stated in my post a few weeks ago, there are multiple species of silk producing insects and arachnids all over the world. Bombyx mori is not even exclusive to China, being native to India as well. What WAS exclusive for a considerable part of history, was the secret of cultivation, specifically, how to break through the cocoon without damaging the filaments, leaving one long unbroken strand ready for spinning or weaving.
If the secrets of silk were discovered in Henan Province, where did it go next? The obvious answer is to OTHER provinces of China, and indeed, the next oldest examples of silk are found in Zhejiang province, among the archaeological ruins of the port city of Liangzhu, dated approximately 2,750 b.c.e. But, if you look at a map of China, there is at least one province between Henan and Zhejiang. There are also a lot of years between the discovery in Henan between 6500 b.c.e. and 2750 b.c.e. So likely, the provinces immediately surrounding Henan benefited next, with evidence of this buried in the sands of China.
While bombyx mori was being discovered and cultivated in China, various species of antherea were being used provincially throughout parts of Europe. Wide use of silk as trade good was known in Europe before contact with those master traders, the Han dynasty, with silk being located as far west as Germany and as far south as Egypt well before the Han dynasty rose to power in 200 b.c.e. However, under microscope, this silk is found to be the uncultured antherea silk, not the highly developed b. mori silk the Chinese cultivated in to art form.
THAT silk, would remain a secret of China until the Han started trading it heavily along the trade routes which later became known as the silk road. Silk became such a highly traded commodity that people paid their taxes with it. But the secret of silk cultivation, while closely guarded for millennia, would be lost with immigration. Cultivated silk next makes its appearance in South Korea, that we know of, with cultivation there beginning between 1000 and 200 b.c.e.  During the Han dynasty in China, Korea was a province of China, so it’s not surprising silk cultivation would have spread there through immigration.
From there, the secrets of cultivation eventually made it’s way to India by 300 c.e., to Khotan in western China by way of dynastic marriage in 440 c.e., and into Byzantium between 450 and 550 c.e. by way of corporate espionage when two monks stole the secret of cultivation and brought it to the court of the Emperor Justinian. Or would that be monastic espionage?
No secret lasts forever, not even secrets that carry a death sentence, and as the secrets of sericulture spread and silk lost it’s novelty value in the west, other trade goods became more prized. But silk always remained expensive and maintained value as a trade good. The labor involved and specificity needed--white mulberry only, not black mulberry, specific climate needs to be maintained, the worms have to be CONSTANTLY fed and their waste product removed immediately…hey, EVERYBODY poops, even worms. Silk has always been and remains to this day, a luxury good.