Spare parts for older n-scale steam locomotives

My train club has two n-scale steam locomotives that run well but are missing parts that make running them impractical. They are a Rivarossi 4-6-6-4 Challenger that is missing it’s trailing truck, and a Model Power 4-6-2 Pacific that is missing it’s smoke box door. Does anyone know where these parts can be acquired?

Hi There! Your economically best bet is to go visit your loco or regional train swap meets this fall and winter and pick up some doner engines for parts. Or look on good old Ebay!