You can get the Galliard-42 XN7568 by completing forges or killing forge saboteurs. This is not tied to any bounties that Ava hands out, as it's a random drop at the end from one of these two sources. Forge saboteurs randomly spawn on either Nessus (Artifact's Edge/Glade of Echoes) or the EDZ (Outskirts/The Gultch).

Where does the Galliard come from?

Performed as the afterdance of the stately pavane, the galliard originated in 15th-century Italy. It was especially fashionable from c. 1530 to 1620 in France, Spain, and England, where it was often called the cinquepace after its five basic steps (French cinqpas).

Where is the misfit Destiny 2?

Source: Open Legendary engrams and earn faction rank-up packages.