This Mote of Shadow farming guide will show you the places that I use for farming Mote of Shadow. There were no major changes to Mote drop rates at Outland, so this guide can be used for Burning Crusade Classic (TBC) and Retail WoW.
Primal Shadow comes from combining 10 Mote of Shadow, so if you need Primal Shadow, you have to farm Mote of Shadow.
Mote of Shadow
The best place to farm Mote of Shadow is at Void Ridge in Hellfire Peninsula. There is a lot of Vacillating Voidcallers and Collapsing Voidwalker at the marked location, they all have really fast respawn time, so you can farm here without downtime.
You can also farm Voidspawns around Oshu'gun in Nagrand. These are a bit higher level than the mobs at Hellfire, and these mobs are a lot more spread apart.