While they are NY based, Fractured Atlas has a fiscal sponsorship program that would seem to be a good institutional fit for a small press project. Check out their Fiscal Sponsorship info page. They also have a list of publishing projects they have sponsored. You might want to conact people at a few of those to see how the experience was.
If you prefer someplace local, you could check through the list for CA at the Fiscal Sponsorship Directory site. One place in southern California is Visions Made Viable in Irvine, which could be a match if your project will have a commitment to social change as part if its agenda.