Having a hard time with finding Master Cylinder

Some of the brake parts on the 1976 Dart and Valiant cars were used only in that year. Chrysler increased the size of the caliper pistons and used a new proportioning valve in 1976. Different master cylinder part number in 1976 compared to earlier years. An old Bendix brake catalog shows part number 11707 for new master cylinder and R11707 for reman master cylinder. These numbers are listed for power brakes with front disc. Might find one of these on eBay.