Lately I've been trolling various postcard collections looking for theatre photos. I recently came across Card Cow - a great site to lose a day on. It's easy to do searches for various areas of the city or specific building.
And if you haven't been there already, do check out Elizabeth Fuller's Old L.A. Postcards collection on Flickr.
Another one with some great treasures is Penny Postcards from California. The view here of the Earl Carroll Theatre is from that site.
You'll find other postcard views of this theatre along with lots lots more information on the Earl Carroll Theatre page that I've recently updated.