I'm not sure if there is much of an industry for it here since it does grow but not at such a prolific rate as it does in Oregon.

You might need to go out and harvest it yourself if you want native species.

If you just want a nice carpet of moss, you might even consider buying some at the store and doing the beer/milkshake method with the blender or buying the milk carton of moss.

What kind of water will you be using to water the moss?
Also how cool an area is the spot during the summer?
And what kind of soil is there?
Not any California "native" moss can grow just anywhere.
Many mosses that are found in other states are also found in California.

You might want to try the moss milkshake stuff (or make your own) first to see if the weather will work with the area. Then, if it takes, you can look into getting various types shipped in so you can have a carpet with various textures.

Thanks for responding, Wizzard. But it sounds like no one sells native California mosses? I suppose it's a strange request, but I'm really into natives. My husband is very successful with mosses on his bonsai, but I don't want Japanese mosses. I'm hesitant to remove plants from the wild, so I think I'm just going to go with a different plan.

Ah, perhaps put an outdoor bonsai there? That can look nice as well.

With moss, you could check your local nursery and see if they have flats of it and ask if it's native. You could also check about your house and the roof to see if you have moss growing there and just transplant it.

I know we have some strictish laws here about plants and wildlife but in the case of moss I wouldn't feel too much of an ethical issue since if it is growing like crazy it probably isn't one of the endanged species. I've seen some poor reviews of places that sell moss online and the reason they got bad reviews was that people found out they go into the wild to harvest their product.