My Dad needs bed-to-bed transportation to get to an appointment, need advice on how to identify good tranportation providers in Los Angeles

I have asked the LA Dpt of Aging and the local Multipurpose Senior Center but they do not provide this sort of service and cannot provide any private referrals. So, does anyone have any ideas on how to identify good ambulance/gurney-van transportation companies in the LA area beyond just doing a google search or looking through the yellow pages? Thanks!