Firstly, I would ask to see the supervisor or for the location of the supervisor's office.

Another way would be to look for a staff member who may not be at the work stations but who may be at a desk or table near the security / customes / immigration area and doing some "office-type" homework like looking over papers like spreadsheets or forms; or simply roaming around the area. Also look for offices that are near the area concerned and knock on the door of one of those offices.