Need outside mirror for '66

[Cymbrogi]

Let's see how I can make this description clearer than mud
The "plastic" plate that goes on the car below the mirror is the same size on both the old model and new. But the metal plate that goes between the mirror and the plastic is considerably different, as is the mirror base and shape itself.
The metal base currently resting on top of the plastic has slits that you can adjust where you put the screws. The actual holes are drilled in at 3 1/4 inch distance from each other. The new model has the holes much farther apart, also the mirror itself is much bigger.
Someone suggested I try junkyards, and then said "good luck!" as if it'd be wasted effort. I don't mind paying money for new, but I want it to fit.