How do I get another officer?

The Officer Recruit is most likely rigged as you can probably notice with your level right now. When you try to check other players on similar Command Center levels (it is safer when you check your corps co-members' details), you'd notice that they all have the same number of officers and even types. The highest chance to earn additional officers can be achieved as you collect fragments (about a hundred for each type) from activities like defeating corps boss battles (e.g. EM Knight, McDevils) -- as they reward a specific Officer fragment. All members that participated the event would normally be rewarded with the same number of fragments each time they succeed in killing the boss. Otherwise, you can opt to collect fragments from counterattack, special ops, and then trading them in the "Military Academy".