I freed some prisoners in vault 3 and one of them gave me the overseers password.
Well I looked all over in that vault and cannot find the overseers office anywhere.
Anyone have any advice on how to find it?

Just keep walking around and check your map often. The Overseer's office should be visible from where you get the password (the round window, up top.) Keep a mental not of its general location on the top floor and you'll run accross it eventually.