My daughter is creating a butterfly garden as a community service project (for scouts). She needs to plant around 30 plants from at least 12 species that are food sources for the larval and adult stages. They are to be native Southern CA plants.

Any recommendation for plants?

Any recommendations of a sources where she can find Southern CA native plants?

Thanks you!

I suggest doing a search for "California native plants for sale". Pick a nursery close to you, or make it a road-trip destination. They could advise you on what would work well.
Milkweeds are for Monarchs, look for a variety that does well in your area. Don't forget to plant nectar plants also. Are you trying for a Monarch Waystation?
Where will the garden be located? Is it at your home or in a public area? What sort of soil does it have, also how much sun? Will there be some sort of watering system? Are you interested in starting some plants from seed? Is there a time limit on getting this going?
Sounds like a great project .

Caroses I suggest she try Butterfly Weed. The variety I planted was Asclepias curassavica. My butterfly population exploded after planting these. I have been able to see the whole cycle of life since planting these. They take our extreme heat and the freezing temps we have also had a few days this winter.

FWIW: https://xerces.org/blog/tropic...

I'm a little late to the party, but I'd still like to help. Louie's and Parkview both carry plants from Moosa Creek Nursery. It only grows Cal natives. You can go to the Moosa site and select plants that they will send to the nursery of your choice. Calscape.org is a fantastic source for plant selection ideas and lists which species of butterflies and moths like which plants. Use one of the Cal native milkweeds instead of the tropical one.
Happy gardening and welcome to the Wonderful World of California Plants!