I, too, am looking for a copy of SMAC-X (for a friend - I have a Windows and a Linux version for myself) for Windows. The site you referenced is out. Does anyone else have an idea?
Marack, if you are able to run Linux, look at the Planetary Pack available from
Loki Software - it's only $29.95 (the original price of Alien Crossfire, if memory serves), and installs and runs like a dream.
Another theory - since the Planetary Pack and SMAC-X both appear to be out of print, it is possible that the Gold edition that is selling for about $10 may include SMAC-X. I'm not sure of this, and would love to hear from anyone who has bought it whether this is the case or not. (I may just break down and buy it myself so I know).