It's more of an inspection port for checking/adjusting the ignition timing settings. You can run without a cap, but it does release some cooling air that should be going somewhere else. Heck, you can even stuff a tapered rubber stopper (like a cork) in the hole until you gain access to the correct part
Maybe someone else up in Canuckland has a spare, or can set up a group buy for a quantity and split the high shipping cost, amongst the needing recipients - just a thought