69 Dart quarter window roller

I need one of these quarter window rollers for my 69 Dart as shown in the picture. Does anyone know if these are available as reproductions or do I need to look for an original? Also, can I replace just the broken roller or do I need to replace the whole assembly? I haven't tried to take it off but is the broken roller even replacable? Kind of looks like it was molded around the pin. The other roller on the pin is in good shape so I was hoping only to replace the broken one.