Hm. I'm not going to have time now to do as good a job as I'd like (I'll have to go to work soon), but I'll get to work on that. All I can guess is that they didn't make the transition from the old site and no one realized it. There were some strange flubs here and there as a result of the transition.
Evidently it's supported in MESS, which I was not aware of. I will keep searching. Seems like most emulators are for the X6800 or one of the other Sharp computers. Have found a few though...if you've any additional information on them that isn't there, feel free to share. I'll admit I'm not that familiar with the X-1.
Hmm...keep finding the same ones over and over, one of which I can't find a download for since apparently the original site is gone now (that would be WinX1). Though they aren't bad, they haven't been updated for some time, so I'm going to guess MESS might be your best bet anyway.