window mechanism parts

My son and I are building a 73 Duster. One of the many problems being addressed are the side window mechanisms. The windows operate on 2 sliding rails with plastic wheels that lock them into the rails. Of course after almost 40 years, these wheels have become brittle and broke off. I have check several places on line including year one with no luck. Anyone out there have any experience finding these….or engineering something that would work?