Hi, Derm.
I'm in the Bay Area. I haven't found any good part sources locally and simply go to the MBZ Classics Center, Authentic Classics, and SLS (Germany). MBZ in Monterey has been able/willing to get an OEM battery for me and I like working with them. There is the PorForAuto salvage yard in the LA area that is a good source of salvage parts and I've used them several times for things like a baffle plate and exhaust header.
Hope this helps.
Rich