Forum sponsor Trainz has the part; it is called the coupler armature:
https://www.trainz.com/product...ectId=43592579743866
Luckily, the trucks on this car can be disassembled for armature replacement. You will need to remove the thumbtack from the broken armature to insert into the new one. I also recommend the application of a small amount of "Goop" adhesive over the hole in the thumbtack mounting plate to securely hold the tack after insertion. These Trainz replacements work very well; I have brought many a Symington-Wayne MPC-era truck back to life with them.