What I need is a Big Rig Non Owner Commercial Policy.

I need the non-owner Big Rig (not auto) policy. I don't own a Big Rig, I only drive for other truck-drivers and get paid for my service. So, the policy I want would cover the truck-driver's truck, trailer and load and I would need Liability too. I only drive Big 18 wheeler Semi (tractor and trailer; no auto) within Southern California limits: no driving out of state, no hazmat and no longer than a week for a customer. My service really is for one day. I could easily be added to the truck-driver's policy, but due to my service calls are at night, no insurance office are open at night. So, I must carry my own Non-Owner Big Rig Commercial Policy. Does it exist, so far I call around and it doesn't, but who can or who is responsible to write up policys? Thank You.