Need a part for the top of a bi-fold mirror door

I need a part like the one in the photos for the one side of a bi-fold mirror door. It appears that the part has a plastic knob on a spring that goes into the top track. This part is on the side that pivots to close the door. The bottom of the part is inserted into a hole in the door and there is a plastic nut that keeps the part secure. The doors have 4 panels that are about 18 inches wide. These doors are at least 12 years old so there are no markings or information on them at all.