The lair can be found in the far south of Talabecland. The approximate location is 44000,63000, south of Dortwald and the Haunted Windmill. To access the lair, you must kill the Unguarded Griffon Eggs in the area until the Bleakwing Patriarch (a rank 40 Champion Griffon) comes down. Engage the patriarch in combat and when he is nearly dead he will use a Wing Buffet that knocks all nearby players onto the ledge of the lair.
Note: Unlock is under live event lairs