IMGUR
After interacting with the book in the library at the back of the first floor stairs and then to the librarian to start a quest chain that leads to the NPC Merindora about this book. It's located at the imagine linked in a cave in the river.

After you find it the first time you talk to the blacksmith in the main town.

Can be obtained by interaction outside of the broken questline - Unsung Hero can't be accepted after the Kama main quest was changed.

You can follow the questline guide made by the other guy in order to find the interaction points:
https://imgur.com/gallery/Co4t1