There were various other things you could get to hold more film than the two-sided holders – the original one was a bag magazine that contained a stack of film holders, and you could slide one out into the bag and stick it in the back of the stack:
http://lommen9.home.xs4all.nl/holders/cut%20film%20magazines.html
Then there’s a grafmatic, which is a later, more automatic spring-loaded version of that:
http://graflex.org/speed-graphic/grafmatic/
There was also a similar system that used pre-loaded film packs (kind of like a polaroid except it didn’t eject the used film), but I can’t find a detailed page for that one, they stopped making the packs for it in the 80s apparently…