If you're in California, I always recommend https://www.laspilitas.com/

They have a couple nurseries but their website has a lot of good info.

There's also https://www.cnps.org/ and https://theodorepayne.org/

Call your local extension from the University of [State]. They have experts that can help you, and probably have programs to supply you with the seeds for no cost.

In Phoenix our botanical garden has information.