CA has an excellent community college system, and many of them have German courses. However, the first semester of a foreign language at a CA community college is typically equivalent to years 1 and 2 of that language at a high school. The 2nd semester is equivalent to year 3 of HS.
Check the online course catalogs of the community colleges near your new home. If there is nothing convenient nearby, you can look for online community college courses at https://cvc.edu/courses/
You are right that German is no longer a common foreign language in CA high schools.