For SoCal I would start with Sportworty here on this site. He's well dialed into the Concours part of the hobby and will be very helpful.
Allot of the yards will not want to deal with the date checking, pain in the a** (their words) hobbyist. Because if this its difficult to get them to check the details. Of course that is why in person visits work the best.
Are you looking for big parts, body sections or little stuff?