FAA 7340.2M HTML
FAA 7340.2M PDF
The full list of FAA recognized (civilian) callsigns can be found in order 7340.2 chapter 3. The letter suffix at the end just denotes revision number.
The nice thing about the way they laid it out is that they printed the big table three times, first sorted by company legal name, second sorted by callsign (what they call telephony), and third by three letter designator.
In any case, in a web browser you can just hit control F to search the text.