Despite my two character playthroughs and over 100 hours spent wandering the Capital Wasteland, I never encountered Reign of Grelok. Apparently it's found on a computer terminal in the Hubris Comics store.
Now it's also found on your browser, courtesy of a remake by Chris Marjason. It's short, as you'd expect from what is essentially an easter egg hidden in Bethesda's RPG, and doesn't require any typing, instead you simply select from a list of canned text options.
But, hey, it's a text adventure inside Fallout 3.
Reign of Grelok [Chris Marjason]