Well, I just did a quick search for D93 on my computer, and ARIB TR-B28
User requirements for a flat panel display as master monitor in an hdtv programme production environment makes several references to it.
Here's a couple of quotes translated by Google:
D65 is D, which is a light source and the color temperature of 6504K and 9305K color is D93
The temperature is used as the reference white of the monitor in Japan. Daylight is the D stands for self - Close to natural light.
(White) Color Temperature Requirements
D65, D93 can display both.
The temperature does not change color when the signal level.
While it does not actually show D93, this image from Wikipedia shows why we use D65, D50 etc.
5000k, 6000k etc. are all lines on a CIE chart, rather than a specific point.
From what I understand, if you can calculate the SPD, you could really have D45, D80, D90, D100 etc. anything from D40 to D250. (4,000k to 25,000k)
E.g. any point on this curve is D something