Film for a 1943 Fairchild K-20

[common man]

I'm looking for film for a K-20 aircraft camera and have been coming up empty in my searches. The camera seems to work, but I've been asked to prove it. The mag takes a 19' 6" roll of 5 1/4" film with 4' paper leaders at both ends. It produces 4x5 negs. I don't need a whole 19', just something that works. Any suggestions would be greatly appreciated.