Why a color grading suite needs high CRI lamps? I'm building a color correction suite. Among the requirements, I read that it needs to be lit using 6500K lamps with CRI 90 or higher. Which are pretty hard to find in my location.

I totally understand the 6500K requirement but why do I need a high CRI lamp? How does seeing the walls and the other stuff in the room in it's "full glory" affects my perception of the stuff on the screen?
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.