There's dozens of private ambulance companies in Orange County and nearby areas. However pay is low, roughly in the $10-15/hr range. The vast majority of companies do only non emergency interfacility transport (taking people to and from dialysis appointments, discharges from the hospital to nursing home, from nursing home to doctors office for appointment, hospital to different hospital because of insurance reasons (*cough Kaiser *cough cough*)). Only a couple of those companies do any 911 response, and those companies still do IFTs.
Care Ambulance, and Emergency Ambulance Service (EAS) have 911 response contracts in OC (there's a couple others who have small contracts for an individual city, but those are typically a 1 or 2 station for the 911 area whole the rest of the operation runs around doing IFT)....but both Los Angeles and Orange Counties, all 911 response is run by the Fire department. Private companies are contracted through the FDs to provide BLS transport, and on scene the Fire Medics (or even the non medic Fire Captain) has full authority and the private EMTs have little scene control and basically get told what to do by said fire medics on all 911 calls.
If you are willing to commute to Riverside or San Bernardino Counties, AMR is the 911 transport provider there. Although the FDs are still ALS there, unlike LA/OC, AMR is the ALS transport. (They'll be staffed 1 and 1 medic and EMT) and are in charge of patient care, supposed to be at least. There's plenty of AMR employees from those areas that can expand upon the actual working relationship with fire in their areas (or lack thereof)