Based on the 1963-1974 Ford Parts Interchange Manual, a 71Montego Upper Control Arm is interchangeable with a 67-73 Cougar (upper). The part is identified as D5DZ3082C. The part is also interchangeable with: 71-77Comet upper; 66-70 Comet/Montego upper; 66-70 Fairlane upper; 70-77 Maverick upper; 67-73 Mustang upper; and 71 Torino upper.
Try West Coast Classic Cougar or National Parts Depot.