Gama Aviation advertises on Climbto350.com web site with a list of cities that are considered home based, most major airports. Last ad had the following listed. I have seen many others over the last few months. BDL, FLL, JAX, MCO, MIA, PBI,
THS, RSW, TPA, ATL, SAV, PDK, BWA, BOS, PVD, PWM, EWR, TEB, ALB, BUF, SYC, ROC, HPN, JFK, LGA, CLT, CHS, ILM, RDU, PHL, IAD, ORF, RIC, BNA.
I believe you would have to live within 1-2 hours of those airports. They airline you to/from your first flight of the "tour" if an airplane is not at your home base.