If contacting a user of these cameras "back in the day" is of any interest to you, Richard C. Miller is still alive, here in Los Angeles, at age 98 (http://www.richardcmiller.com/).
His film holders (5x7) had built-in filters. (I know this because I have seen them in person.)
He used a National Lerochrome camera like this one (a measly 3x4, though it is very neat that it is a tungsten model): http://www.collectiblecameras.com/pr...cat=350&page=1. It is now owned by his assistant.