You can also get them from: https://www.darkcoin.io/masternodes.txt http://drk.poolhash.org/darksend.html
If you are going to do it manually I would wait for the hard fork (mid June) because the lists that appear now are not accurate. Some of things that are being fixed now are related to propagation of this information through the network. If you plotting updates automatically, then you can use any of those sources and when we do the hard fork it will update.
I don't mean to be unreasonably demanding but just to give an idea of what I was thinking regarding the rotating globe, check out the NASA "night lights" video. It would be great to make something similar for the masternode network - a dark globe being lit by flashes of connectivity as the masternodes do their work (my apologies in advance for being incapable of doing this myself - it's easy to have ideas...).