AMK carry's the zinc plated washer under their P/N of B-13036 but not the nut.
They have a $30 min order. The washer doesn't look special so you may be able to get a duplicate at a good hardware store or Home Depot.
The nut is likely a standard one though my guess is it's probably the square shoulder type that is characteristic of original hardware and the new ones today have a slight radius.
Mike
