Here is the SAI campaign editor for download. Put it in the SAI directory.
Note! The campaign editor is provided free for users of SAI. It is provided as is with some rather minimalistic documentation (in the zip file). While it has a lot in common with the scenario editor, it is not all that user friendly, and you should be aware that creating and testing campaigns is complicated and time consuming and not very forgiving of errors. While I will try to answer questions on campaign design, time permitting, there is no guarantee of any support or help for the brave souls attempting to create their own campaigns.
For guidance, you are recommended to load one of the existing campaigns and study it.