The Princes of Sartar were road builders. Each of the royal roads are four to seven meters wide and usually rests upon a foundation of rammed soil and rubble one to two meters deep. The surface of the roads are paved with polygonal stone slabs with curbstones on either side. These roads run in straight sections, with no curves, and traverse their way up steeper slopes. At intervals, the road widens to allow shrines and wayside rest stops. Watchtowers and guard posts are spaced along each road.
The silk is taken from Kralorela and Teshnos to the Holy Country by ship and then overland to the Lunar Heartlands, or from the Kingdom of Ignorance to the Lunar Heartlands by land.
Ironically, you are more likely to find Silk Pajamas in Sartar than in the Lunar Empire. If Sartar gets about one ton of silk a year, and the Empire, with 40 times the population, gets 6 tons – well you can do the math.
Is spidersilk from Kingdom of Ignorance still a thing? I suspect there is far more spidersilk produced in Dagori Inkarth (held to be superior for making of ropes and threads than the silkworm silk of Kralorela and Teshnos) than from Ignorance. But it is also produced in much smaller amounts, coming only from the Aranea Cult.
I suspect that silk is also made in the East Isles and no doubt there are intrepid Dormal cultists sailing to Haragala, although that trade may also be going to Fonrit and Maslo.
The Vikings were at a far end of the Silk Road. Remember that Sartar is essentially Bactria here.
Is Troll produced spider silk a thing? yes, and it is stronger than silkworm silk but it is expensive, and not produced in the sort of volume silkworm is, so is less useful for fabric. The trolls traditionally use it for ropes, nets, etc.
Why is Kralorelan silk so important? Surely the presence of the Gorakiki Cult in Dagori Inkarth would present access to the raw material, including spider silk. it is much easier getting silk from a worm than from a giant spider. Even if that spider is a member of your cult. The spider at the very least needs to be persuaded not to kill you.