We posted our USX: Apocalypse rules in the Post-Apocalyptic Tales forum.
However, there is much cross over in these rules for Cthulhu Mythos factions.
For instance, you can play the Mi-Go, Hasturites, Cultists and Elder Things as factions.
If anyone is interested please see the link and let us know how it looks. This is definitely a Beta-Test set of rules rather than a completed book but it is available in .pdf form at our forums. Enjoy!
Link to Lead Adventures thread here, with pics
http://leadadventureforum.com/index.php?topic=68804.0Link to our forum and the free .pdf download here
http://rafm.com/phpbb3/viewtopic.php?f=12&t=612