The California State Archives provides selected legislative history materials from 1940 forwards, available for a modest copying fee. It is usually the best starting point for a reasonably comprehensive, reasonably cheap collection of legislative history materials for a California bill.
The Witkin State Law Library has an extensive collection of California legislative history materials, including Senate and Assembly bills from 1867 forward, Bill Fill Analyses from 1975 forward, and historical copies of the California Codes from 1872 forward.
The LA Law Library, located in downtown LA across from the Stanley Mosk Courthouse, has purchased a collection of Senate Committee Bill Files from the California State Archives.
Purchasing Legislative Histories
Several companies specialize in California legislative history research. You can purchase an already compiled legislative history or pay them to compile an original history.
For quotes and more information, see the companies' websites: