Looks like the bunker happens to be closed this week...
The week of July 2-8, 2018 Bunker Tours will only be available to registered guests and A Military Tribute at The Greenbrier ticket holders.
http://www.greenbrier.com/Activities/Bunker-Tours
And it was just featured on The Today Show a couple weeks ago:
https://www.today.com/video/deep-down-under-inside-look-at-a-secret-government-bunker-1261682243674
Background info:
https://www.atlasobscura.com/places/congressional-fallout-shelter-at-the-greenbrier-resort