Alternative journal entry:
The Banner of the First Regiment, a turian artifact, was recovered from Castellus in the Apien Crest. Find someone on the Citadel who can use it.
A group of three turian officers can be found chatting inside Purgatory, in an alcove to the right of where James is located at the bar. Listen to their conversation to acquire the mission.
Alternatively, you can also acquire the mission if you choose to conduct Search and Rescue operations in Castellus. This second way of acquisition is possible even before the Purgatory becomes available on the Citadel. In this case, the journal entry for this mission is named Citadel: Banner of the First Regiment.