My favorite place for farming sturdy hides is at 7.9 S 40.0 W in Esteldin. it's SW of the entrance to angmar in nan amlug. There's a couple little ponds with a bunch of level 33 or so signature hoar mantles that drop about 3 sturdy hides each. there are a lot of wargs around the area that you can farm while you wait for the hoar mantles to respawn.