Many People in the Balearic Islands use sisal yarn als is used for straw bales. Its available and rather cheap. I acquired a large roll recently and made a suitable balearic split pouch sling with it. Diego Camuñas does use only use short and thin pieces of around half a meter, and twist the strings while braiding, and add new pieces of string often. The new pieces are untwined, and twined again togetherwith the pieces of string tzey are added to.
If its allowed, here is an example, I am not connected to the seller in any way. More than a kilometer for 30 euro, relative prices decrease even mor with larger rolls
https://smile.amazon.de/Sisal-Pressengarn-Bindegarn-Sisalseil-Sisalkordel/dp/B01G3K0E9W/ref=mp_s_a_1_4?crid=234LE5ZL9GR68&keywords=pressengarn&qid=1666888076&qu
=eyJxc2MiOiI0LjcxIiwicXNhIjoiNC4xNiIsInFzcCI6IjMuODQifQ%3D%3D&sprefix=pressengar
n%2Caps%2C130&sr=8-4