I'm surprised no one has mentioned Agfa in this thread. I picked up an Agfa Isolar with only one double sided plate holder. I've had no luck searching on my own and would appreciate if anyone could point me to a thread or site that explains how to make a film sheath for the plate holder.
I'd also like to see other Agfa 9x12 owners speak up here. I'm about to start my quest of buying cut film holders off that auction site in the hopes that eventually I'll get some that fit. I'll add some photos and measurements of the lone plate holder I have in another post if anyone is interested.