Instructions: Order & Destruction
Kill 'Wyrmstone Chargers' (not 'Wyrmstone Boars') just outside the Dark Elf Chapter 15 at 2k 20.7k Caledor until you get Pocket Item 'Lean Boar Meat'. Equipping it will trigger the unlock.
Once the unlock triggered, you can claim the jewel buying it from the correct merchant in Library (Order) / Lyceum (Destruction).
Note: The drop rate is low (10%).