Yesterday I created a simple API to get the closest NCS of a hex triplet (and then the hex triplet of that NCS). I later expanded it into a site where you can use the API without implementing it yourself and see the color it locates.
You can find the site at http://code.maxmalm.se/ncs/
Yes, I know the image refers to the Pantone color chart instead of NCS.
The site uses Kimono Labs and Encycolorpedia to serve you this data.