Welcome Wigabee
If you decide on using GWX3.0 you will find it contains 58 single missions and 41 multi missions.
These were created by a variety of people myself included.
I usually keep an unmodded (no additional mods) installation of GWX3.0 for testing and mission building purposes on my system and as such would be happy to build/create a few for you if you wanted.
Simply inform me of the historical/hypothetical detail you would require.
Remember though...for them to work you would need only the basic GWX3.0 added to stock/vanilla SH3.