Hi!
The Sturmmoser is not in the Combat Mission, simply because it's a really long range weapon, and it doesn't fit into the scale of CM maps. It could be work like off-map artillery. I think it fired 300mm rockets, and there is a 300mm rocket unit amongst the artillery weapons. So, if you want very much, there is a Sturmtiger in CM, it's just invisible.
109 Gustav: The Sturmtiger was service on the western front. I saw many of pics, where US troops looking at abandoned, or self-destructed Sturmmösers. You may confused it with the Elephant/Ferdinand TD. It was the Tiger based vehicle, which saw service only on the eastern front. (OK, some unit stationed in Italy in '43, but that was the only exception.)