Tag and Bookajet have got large fleets, but not all are G-Regs or are on their own AOCs.
Eurojet have a few machines I think.
How many machines in the Air Partner fleet at the moment?
LEA must be up there, when you consider the numerous Mustangs, plus a couple of King Airs; CII/Bravos, XLs, Challenger 300s, Legacys and the Falcon.