Thats 5K officers, Regular and Reserve (Primary Reserve and Cadet Instructors)`, so the pool is greater than just people assigned to CMS.
For example, joint organziations like the Chief of Military Personnel, Assistant Deputy Minister (Materiel) and the Vice Chief of Defence Staff all have many members who wear the Navy DEU, but are not part of the Chief of the Maritime Staff establishment.
If you are internal to DND, look for the DHRIM website; there are statistical reports available that are updated daily, with month-end reports archived and available.