The blue and/or pink foam is available in California. No, Lowe's and Home Depot don't have it, and it is rare that they will special order it for you. The lumber yards and/or builder suppliers are the places where it can occasionally be found or special ordered. I believe Pacific Building Supply is one such place (actually a chain). There was an independent lumber yard in San Rafael that carried both the foam (in a variety of thicknesses) and Homasote.
Builders, carpenters, and wood workers looking for quality lumber and supplies don't go to Lowe's or Home Depot, either.
Consult the Corning and Dow (makers of pink and blue foam) web sites for non-big box dealers, and then call them. You'll find Lowe's and HD are listed as dealers; ignore those listings. The same process works for finding Homasote.
I always get tickled by the assumption that if Lowe's, HD, or WallyWorld doesn't carry something, that it doesn't exist. Or that if they don't have it, it must be illegal in California. We lived for decades before the big box stores arrived, and we could probably survive without them again. They are just an easy single source location for cheap goods at a cheap price.