First we should clairify, are you refering to Mars: World at War which is currently being developed for the UWZ edition of warzone and has not yet been released, or are you reffering to Capitol: Forces of War which was released some time ago but contains second edition rules and information, which is not compatible with the current UWZ ruleset. I know Capitol: Forces of War contianed some McCraig line specific units for capitol, and I am confident that when it is released Mars: World at War will contian information on units fighting on the McCraig line on both sides, Imperial and Capitol.
Its possible where ever you saw this advert, they were selling the second edition book with an estimated delivery time of 3-5 weeks? Thats all I can think of since, as Joe pointed out, there have been no rules supplements released for UWZ.