Try the local airport control towers.
123.300 and 123.500 are set aside for use by hot air balloons, and gliders/sailplanes. Air-to-air and air-to-ground.
CB radio; 151.505; 151.625 Red Dot; 151.955 Purple Dot; MURS (technically illegal as these frequencies are specifically prohibited for use while onboard aircraft); FRS/GMRS; 464.500; 464.550; several 467 MHz frequencies; Ham radio.
If your scanner has signal stalker/close call capabilities, find their launch sites and look for their pre-flight or initial launch radio checks. Or just ask the crew members

(I used to be one here in AZ for a decade+.)
John
Peoria, AZ