After completing The Fremennik Isles
, Vanligga Gastfrihet
will sell you 20 Yak-hide packs
There are multiple ways to get to Jatizso, but the easiest are using a Rellekka tablet and running north to the Rellekka dock, using the Fremennik Lodestone, using the Lunar Isle lodestone and using the Lady Zay and Lokar Searunner to get to Rellekka, or by simply toggling the Enchanted lyre teleport to Jatizso, after completion of the elite Fremennik Tasks.
Once on the island, head to the store and purchase the 20 Yak-Hide packs. Additionally, one can use Surge
to travel nearly instantly to Vanligga Gastfrihet
by moving one square northwest from the square immediately north of the banker Magnus Gram and using Surge. Alternatively, by clicking on Vanligga and immediately using Surge. After you have bought all of them, you can sell them on the Grand Exchange
, where they should sell quickly as they are popular Summoning tertiaries.