On October 28, the California Secretary of State posted the list of declared presidential write-in candidates. See it here. Only five candidates qualified. The state requires notarized forms to be signed by each candidate for presidential elector, and will not accept a filing without 55 candidates.
Bernie Sanders is on the list. California is the only state in which a write-in slate of presidential electors may file without the consent of the presidential candidate whom they are pledged to. The same procedure was used in California in 2008 and 2012 to cause write-ins for Ron Paul to be counted, even though Ron Paul did not file himself and had no wish to be a candidate in November of either year.