Between my spare parts kit and the machine maintenance kit, I've found a spare for just about every small part, except for the bowed washer, Part 14041.  Somehow, I've mislaid mine over the times I've replaced the bellcrank cube or other machine maintenance.  I think that would be something to consider including in the spare parts kit.  As for the other washers, such as #10 or other flat washers, those are easily procured at a hardware store, but I have never seen the bowed washers there.