I think there are many available options.
My older daughter just graduated from Tulane with a dual degree in Music Composition and digital media production. She was initially unsure if music was going to be her focus and wanted to keep her options open. It became clear very quickly that music was her passion. She was very happy and has no regrets. Tulane’s music department is small but very good. And very supportive of her and her work.
As a fellow resident of the great State of California, I’ll echo what others have said about solid options in the state (besides USC Thornton) for what you’re looking for:
And if he doesn’t get in to his preferred program(s) and composition is truly his passion, the JC route to get to one or more of those schools is a truly viable option. I know multiple students – and particularly one UCSB composition student – who went to a JC for a year first.
Is he limiting choices to California?
My kid avoided all schools with instrumental auditions for composers, on principle!
Have you/has he read the Double Degree Dilemma essay in the Read Me thread closer to the top of this music forum?
Another option is to get a BA, in music or something else, and continue with lessons and extraccurricular musi.
I can tell you that the best grad schools have students from all kinds of educational backgrounds.
Finally, the composition programs may not be as competitive as you think. Fit is important.
The hard part for concert composition is having access to musicians to play pieces written for the portfolio.
I am going to PM you.