SquawkBox has to have access to several data sets in order to work properly. These include ICAO aircraft equipment type codes, ICAO airline codes, and geographical information on the location of aerodromes throughout the world.
Below are two locations for this data that I have found very helpful, so I thought I would list them here:
FAA Contractions: Includes a comprehensive list of ICAO codes for aircraft equipment and airlines worldwide
Digital Aeronautical Flight Information File (DAFIF) Data: Comprehensive geographical information on airports, nav aids and much more, provided by the US military's National Imagery and Mapping Agency.