I went looking for a replacement 70W MV ballast for an existing fixture and my lighting vendor said that a Metal Halide ballast will fire a MV lamp just fine, and that the only way he could get an MV ballast was to try and find old stock somewhere. I had to try it because there are another 15 fixtures, and swapping them all out for Metal Halide was not an option.
It actually worked very well, and has continued to work for several months.
Looks like, yes, MV are going the way of vinyl records.
