I lived in Uzbekistan for two years. They make a lot of silk cloth there. They're along the 'silk road' and any silk going to the island likely went through there.The Uzbeks tell a story of how a princess smuggled silk worms out of China in her headdress to start the silk trade in what is now Uzbekistan. The Indians have a similar legend. Given that current political lines between countries were unknown in ancient times, I expect the shared legend refers to the same princess. I know this really has nothing to do with British History. As to the trade, yes, the silk had to travel a very long way to get to our story, but it is incredibly light and packs into a very small space. I should think it would still be profitable to transport it all the way. While it would certainly have been a luxury item, I expect it may not have been as rare as you might think.