I made this Callous Hide farming guide to help out players who want to farm the leathers instead of buying them from the Auction House. I traveled around the Shadowlands to search for places with a high density of mobs which I can kill and drop Callous Hide. Below you will find a list of places I think are the best for farming Callous Hide.
All skinnable mobs can drop the 5 new skinning materials, so you will basically farm the same mobs for every leather.
Callous Hide is a rare leather that you can skin from any skinnable mob in the new Shadowlands zones.
Callous Hide
Don't forget to enchant your gloves with 
Enchant Gloves - Shadowlands Gathering! This enchant brings skinning time down from 1.5 seconds to 0.5 seconds. (works with herbalism and mining too)
Bastion - 1
Gilded Cloudstriders respawn rate at the marked area is really fast and you can often pull 7-8 together. They spawn on both sides of the hill, so make sure to go to the other side too.
Bastion - 2
Farming Languishing Etherwyrms and Starved Etherwyrms around the marked area is also a great way to get a lot of leathers. They are needed in one of the starter quests in Bastion, so this area will be pretty busy at the start of the expansion. (which can be good if no one is skinning them)
Maldraxxus - 1
Follow the red route and kill every Neonate Bonetooths, Bloodskin Tauraluss, and Furious Alphahoofs. These mobs have a bit more HP than other mobs, but you can often pull 6-7 together.
Maldraxxus - 2
Kill Virulent Pests around the marked area. They are a bit spread apart, but the respawn rate is fast, you will never run out of mobs to kill.
