That looks like the same refrigerator
door opening as my '72.
Honestly the "factory made" one is pretty crude, it's just a sheet of thin aluminum (think aluminum siding thin) with louvers punched in it then attached to an aluminum frame. It has screening on the inside to keep the bugs out. There is a hinge on the top of the frame similar to the windows
, other than that there is no hardware to hold it open and 2 sheet metal screws hold it closed at the bottom.
I think someone with any fabrication abilities could easily make one just as good if not nicer that the oem part.
Mine actually has a split running horizontally thru the louvers due to how thin the panel is.