I don’t really know. Web Archive is useless for this since Twitter authentication is required. Researching options, there may be something out there.
Gotta believe those three major players WERE following HRC, if only for appearance sake. Quite conspicuous that it was noted somewhere that ALL THREE now do NOT follow her.
There is a google cache of that page from August 24, 2016. At that time Warren was following 252 people. However, Google didn’t cache the entire page so you can’t the complete list from that date.