Where to purchase King's Thorn
King's Thorn is a reagent we'll need to create Bayle's Delight, one of the Brewing subcombines that we need in order to make Qeynos Afternoon Teas. You can purchase King's Thorn from two places, one in East Freeport while the other is in Steamfont Mountains. Both of these locations are shown below with map locations.
East Freeport is available to 'Good' aligned races.
Steamfont Mountains is available to 'Evil' aligned races (the gnome that peddles the goods is a Bertoxxulous worshipper).
Quareran Borius - East Freeport (King's Thorn Vendor)
Quareran Borius is found in northern East Freeport inside of the tunnels that surround the arena. From what I can tell he's on the 'good' aligned faction of East Freeport.
Ennixy Frennor - Steamfont Mountains (King's Thorn Vendor)
Ennixy Frennor is found almost directly north of the windmills found in Steamfont Mountains. If you travel directly north of the eastern most windmill you'll find Ennixy Frennor alongside the cliff; shown in the map location I have above.