I do not think that this spheres are coated with GITD stuff. I think it is some kind of white matte color to ensure the light will be reflected into all directions.
The original HDS white diffuse reflectors are also a little bite more diffuse than the HDS GITD reflectors. The only exception is the Firefly since the surface structure ensures a extreme diffuse reflection.
But anyway the white diffuse and the GITD reflectors done by HDS are all not easy to find.
Maybe when I have time I will make my own white diffuse reflector. I would have everything (airbrush, white color, ...), but as always lack of time.