Walter T. Weller wrote:
Dear Walter:
It is not easy to find a queen especially if it is unmarked and the
population large.
Whenever I am going to replace a queen I always follow the following
procedure.
First, make sure that there is a queen (presence of properly laid single
eggs in the cells).
1.  I take the hive apart.
2.  Place a queen excluder on the bottom board and replace the first
brood chamber.
3.  Place a white cloth (a piece of a sheet will do) in front of the
landing board.
4.  Remove the frames one by one and carefully shake them on the sheet
watching carefully for the elusive queen.
5.  Place each frame that has been shaken into a empty brood box. Do as
many brood boxes as you may have.
6.  Examine the walls of the brood chambers for the queen.
7.  If still not found, remove the brood chamber and look under the
excluder.  Sometimes the queen will elude our first scrutiny, but will
become trapped under the excluder.  Usually you will find it surrounded
by a small group of bees.
Good luck.
Best regards.
Dr. Rodriguez
Virginia Beach, VA