Thick Leather is the second highest level Leather from the original WoW. It can be skinned from creatures between level 39 to 55 (to 80 in Battle Grounds). The best place to farm Thick Leather would be Blackrock Depths near the entrance. There is a little route where to follow to aggro all the Bloodhounds, from there head back to the entrance where a vendor is conveniently placed. Very useful to empty bags. Each run may produce up to 50 or more Thick Leathers.
See below for the route to aggro all the Bloodhounds to farm Thick Leather.
Tanaris (220- 250) (level 44- 48)
1. Blisterpaw Hyena, Glasshide Basilisk
2. Rabid Blisterpaw, Glasshide Gazer, Duneclaw Stalker
3. Sand Slitherer, Unearthed Fossil, Sunburst Adder, Duneclaw Broodlord