* At about 1745 gametime go to the Airport Manager's Office and bid for 
  the Branch Offices available, Stay in the office until the end of the 
  day. When you return to your office the next day you will find that 
  your bid's for the Branch Offices were successful.

* Continue doing this and eventually you will have all the Branch 
  Offices available to you. 

* This prevents your competitors from buying the rights and when you 
  have all of the offices in your file you will never have to fly empty
  from an airport in order to collect passengers from another.