Two ways to make some extra money as a skinner (if you're a warlock like myself you can just round them up --> Seed of Corruption and then dot them up OR get a (frost)mage to AoE the living cr*p out of them.
1)In Nagrand, slightly west of the Horde city, there is a huge field. You can find Clefthoof bulls there. (And you can find them under the Laughing Skull Ruins). They drop Clefthoof Leather & Knothide Leather (both with a VERY GOOD drop rate)
2)There's another place in Blades Edge Mountains that is passed the far north mountainpass, only accessible by flying mount. They are 70-72 level mobs. Amber Clefthoofs I believe they are, but their droprate on Thick Clefthoof Leather, according to Wowhead, is better than that at Nagrand. So if it's overcamped in Nagrand, I sugguest going up to BEM.
-Draz