I'd try cutting the pivot pin off flush, drilling through the center of where it was, then fitting a new steel pin, drilled through the center to accept a machine screw from the other side of the handle.
^^^^, drill dead center on both parts a bit oversize for a roll pin. Mix up some 5 minute JB weld for metal and coat everything and stick it together. Hold until it cures...
There are several whole vent window assemblies on ebay that include that piece. Maybe put a wanted ad on here. Should be able to find a replacement pretty easily.