There is an area of town near me that has lots of these fixtures and they mostly all run mercury or metal halide lamps; Does anyone know if these are super rare/old?

I will say those look very vintage and they probably retrofitted them for hid

Ah okay, good to know!

 GE Novalux ??

Oh yes it looks like it

Something "modern" in my experience but there's a small chance they are antique. These are copies of Westinghouse ornamental fixtures, but I don't know how old or manufacturer. GEs have a much different canopy.