In the Bay Area I'd ask Magnani. No idea re. Socal, sorry,
but there must be poultry-specialist butchers you can ask.

Fresh duck liver is certainly a treat. Better than any
"California foie gras" I've ever had. It would not surprise
me if, given the limited demand for and, therefore, production of
ducks in California, that the livers are scarce; perhaps
snapped up by restaurants making duck live flan and similar.

Steve