Before we get too far into this...
Do you have a 53 first series or a 53 second series?
The first series uses Huck Style brakes. The best source for these is a junkyard. AFAIK, nobody makes emergency brake shoe hardware for anyhting bigger than a 1/2 ton anymore. (which really grates my cheese, because I've got a '46 3/4 ton with the same issue).
53 second series has Bendix (AFAIK) and you may (or may not) be able to find that hardware at the various vendors. Have you looked at American Classic and The Parts Supplier Formerly Known As Chevy Duty?
