Hi Dianne! Congratulation
s for buying Brownie from Dave! He's put a lot of blood, sweat, and tears in that wagon... and she's a beaut!
If you have an O'Reilly's or other car store, they have a section with Help! parts. They tend to be packages with red cards that the plastic is attached to, and they carry everything from older car window cranks to interior panel fasteners. If you have a junkyard around, that's another good place to look- but sometimes the cranks and other pot-metal stuff (like inside door release levers, etc.) are in even worse shape than yours! Good luck!