Looking at the Robert Kaufman page for their Kona Cottons ... Midnight #K001-1232 still appears to be a very dark blue, so I don't think they've changed it. I was kind of skeptical that Kona would change the names of their colors and re-use names for different colors ... just not logical. Wondering if the fabric you are getting from others isn't really Kona Cotton??
If I were you I would contact Kaufman and verify that "Midnight K001-1232" is a deep dark blue with no hint of purple. If so, inquire where you can order it, and order it by the number, not the name.
However, if you can't find it, there are three other colors that appear to be very close: Nightfall, Nautical and Indigo.
Here's the Kona page with all the colors
Good luck!
http://www.robertkaufman.com/fabrics/kona_cotton/#tabs