Best place to get thick leather in Darkfall New Dawn I have found to be the Ogre Bosses on an island northeast of Thorsland. You get three ogre bosses at a time. Melee the champion at your own risk. 
Ogre Bosses give one or two thick leathers every time as opposed to the Frostwalkers that only give a thick leather once out of every three times or so.
Interesting I might have go back and try them I typically hate dealing with ogre.