Prothane Spring hanger bushings

[40cpe]

I have the original type rubber in a steel tube type of spring hanger bushings in my '57 springs. The rubber is breaking up in them and I'd like to replace them with the plastic type that slips in from each side. I don't find any sources for them by searching web sites and catalogs. They need to be 1 3/8" OD with a 7/16" bolt hole. These are for the front hanger of the rear leaf springs. Any leads will be appreciated.