Why a color grading suite needs high CRI lamps?
The truth is that you do not need them... unless you do of course.

You only need good CRI for the ambient lamps if you need to compare colors with real-life things, probably the skin tone of someone, or want to prepare the color for a tomato that looks healthy but not oversaturated. 

Another reason is that you can not work totally isolated from ambient light, your eyes will stress a lot. So the ambient light will hit your hands, your keyboard, and things on your desk. Having a low-quality light illuminating this could alter your perception of colors and force you to make wrong adjustments.

If you need lights with good CRI get some on an online store.