Rear Bumper Bracket Gaskets

On my 1972 Dodge Dart Swinger, removed the rear chrome bumper today to have a dent repaired during the winter. The chrome bumper is held by a 2 brackets which are mounted with 6 bolts to the body of the car. Between the brackets were black paper like gaskets for each bolt hole. Does anyone know where I could find replacement for these paper gaskets?
make them out of very thin foam rubber, like used in shipping wrapping. that`s what 68 barracudas had for the gaskets.