The Orb of Unity was recovered from an Obsidian Order storage facility on Cardassia along with three other Orbs by Yevir Linjarin in August of 2376. (DS9 novel: Mission Gamma, Book 4: Lesser Evil)

In September of the same year it was used by Elias Vaughn for his second orb experience (DS9 novel: Unity)

Bajoran Orbs
Orb of Contemplation | Orb of Destiny | Orb of Memory | Orb of Prophecy and Change | Orb of Souls | Orb of Time | Orb of Truth | Orb of Unity | Orb of Wisdom | Orb of the Emissary