Sure you can buy and plant them. You just can't go pull one out of a wild area and carry it home.

Here's a list of places that sell CA native plants

Here is a link that might be useful: list of CA native plant sources

There are many varieties of manzanita and some are considered threatened. But the more common varieties are very abundant in California and other places and not at all threatened. Much of it grows overcrowded to the point of being a fire hazard so in many cases digging one up wouldn't be a problem as long as it's the abundant varieties.

Here is a link that might be useful: manzanita branches

Does anyone know where I could buy some Manzanita branches? I need them for flower arrangements.