I don't think there is any rotorwing based out of Humboldt County. There is a Fixed Wing ops that works out of Eureka and Crescent City. But rotorwing come over from Redding or up from Ukiah. In their primary operating area there are some wide-area high-level remote bases CalStar and Reach use for logistics outside of their cell/sat phones back to their dispatch. Check out
CA Statewide for channels to try nearby. None with Humboldt County coverage though. Otherwise for incidents they'll be on whatever the incident tac is, likely CALCORD, and whatever EMS channel their patient's hospital is on (Medcom channel, satphone, etc.)