Here you can find the list of mobs that drop/spoil it :
https://l2.dropspoil.com/item/2140/recipe-high-grade-suede.html
Tracker skeleton no longer exist in ruins of agony on L2 classic, i have tried on ratman hunters and lycanthopes and so far nothing... i have spoiled like 100 lycanthropes and only leathers and leather helmet designs. Ratman hunters only gave me anibal bone fragment (like 60% of the time) that is not supposed to so I guessed that the spoiled items have been changed.
If anyone has been able to get it somewhere feel free to share !