Driving school is going to be a tough find as their equipment meets the standards/definitions for a commercial class A and not the non-commercial class A. Most rental trailers will be stamped with a GVWR of 9,999 lbs. to avoid the hassle of a special license. The only CA license I am aware of that doesn't require you to be accompanied by a licensed driver is the class M.
The driving schools may not be available for the training but they are in the business of making money so they may have someone that will accompany you for a fee or possible do a side job of training. Stop by in person and one of the instructors might be able to help. I have also heard of people stopping by a local truck terminal and finding a licensed driver that will help for a small cash fee.
