The NGA database can be difficult to search for a specific color if you use the Flower Color selection area. After going into Search by Characteristics try typing the color you are looking for in the Color Description box just below Bloom Form. This brings up 3000+ diploids with "purple".
From what you've said it sounds like you are looking for a full form rather than narrow form diploid purple. My first thought was the Shooter daylilies, Eliezabeth works with diploids and has both full and narrow form purples. Their website show the ploidy along with the images so you don't need to click each daylily to see if it is a diploid. Here's a link to their website...
http://mariettagardens.com/Int...
A favorite of mine from Elizabeth is Tuxedo Whiskers, although it may be narrower than what you are looking for and the color changes depending on the temperature.
