I've only had experience with the 1/4 scale statues from them, but generally they show up on the Sideshow site first in the exclusive form right alongside a standard release, the exclusive version is only available through the site and it goes quicker than the standard version. In the 1/4 line, I've been careful to order the exclusive version right away, since the windows are so short. However...
If I recall correctly, on the first 1/4 scale figure, they used preorder response to gauge the production run. This looks like what might be going on with the 12" line as well.
If you just want to order one without the gun you could just wait until they show up at other retailers.