Here are two links for DMV information, One for CHP (California Highway Patrol), and one for the National Truck Equipment Association. Regarding the NTEA, any body company of any importance is a member of this fine organization. Their website has a wealth of information for you about standards, good practices, etc. I use it a lot to help dealers find specialty body makers and distributors. Let's say you need a glass body for a local glass company, here is where you can find all the companies who make that kind of body or distribute it. Check all these great site out!
State of California DMV Commercial Drivers License Information Publications