Instructions
Begin the second Mark-Hunting side-quest and talk to Gatsly in Sandsea. Defeat the Thextera in Galtea Downs and return to Gatsly. Go to Muthru Bazaar and speak with Gatsly again. Visit a shop and check the Bazaar Goods menu. You will see a Forgotten Grimorie available for 18,000 gil. Purchase it to receive the Hunter's Monograph.
Go to the Great Crystal area. Defeat the Ose enemies to obtain Coeurl Whiskers. Utilize the Steal and Poach abilities during the battles for additional opportunities to receive the item.
Go to the Uazcuff Hills area in the Tchita Uplands. Explore the vicinity before the Eastern Save Crystal. There will be a 10 percent chance of a Grimalkin appearing in place of a Coeurl. If there is no Grimalkin in the area, run two zones away and return for another chance. Repeat the process until a Grimalkin appears. Battle the Grimalkin and steal a Coeurl Whisker during the fight.