This quest/content can be acquired by purchasing it separately or by purchasing Item Pack 2 DLC. It will be automatically unlocked at any point of the game or at the beginning of The Destruction of Lothering quest although its only possible to complete this in Act 1 onward.

To complete this quest during Act 1, you have to go to your Uncle Gamlen's Home in Lowtown  and enter the southern room. During Act 2 and 3 you can find it in the northern room in Hawkes Estate in Hightown. From there you can find a chest marked as The Royal Collection containing multiple items that includes the following axe's (Bard's Honor and the Fiona). The following armors (Arms of the River Dane and The Arms of Mac Tir). The following helmets (Helm of the Vanguard and King Maric's Helm). The following gloves (Freeman's Gauntlets and The Queen's Guard). The following boots (The River Trudges and The Path of the Wilds). The following belts (The Adherent's Belt and The Refined Gentleman's Sash). A bow named The Longbow of Avvars and an amulet named the Pearl. Upon taking these items, you'll complete this quest and receive six codex entries (The Longbow of Avvars, Bard's Honor, Arms of the River Dane, Fiona, Arms of the Mac Tir and King Maric's Helm).