After a few hours of play in Ghost of Tsushima, and after getting your first pieces of armor, you've certainly noticed that silk is very rare and essential for final levels of improvement at the armorer.
Silk is one of the rarest materials in the game, and the means to obtain it are limited.
Complete side quests
The main way to obtain silk at the beginning of the game is to progress through the stories of Lady Masako and Ishikawa-sensei. Steps 2 and 3 of their respective stories will allow you to obtain 2 silks each time, for a total of 8 in Act 1. Other similar stories in the following acts will allow you to obtain more.
Open your eyes
Unfortunately, it is very rare, but sometimes silk is lying around in the big Mongol urts, temples and villas. We suggest to search the premises and pick up anything that can be found by repeatedly pressing R2. Silk looks like richly colored and well-folded clothes.
Only one vendor we know of offers a little silk in exchange for supplies. Once the town of Komatsu is freed as part of Yuna's brother's quests, go talk to the trapper and check out his goods.
Original content by Robin "Raiden" Bouquet.