You can create your own Instant Action missions using the beta Mission Editor.
First get the mission editor here:http://www.franva.org/download.php?list.2
There is a help file in the program which introduces you to the basics, so I will just add what I have learned, the hard way, about the mechanics of using this editor to create your own missions. Remember, it is a beta and was never completed.
1. Backup your existing quick.dat file and BFIELDS folder before you start. If you lose it, you will have to reinstall from CD or game download.
2. Create new missions by copying existing missions (using the copy button) and modifying them. The newly copied mission goes to the bottom of your IA menu and you can rename it to anything you want. You can play with these as much as you like to try to change aircraft types, altitudes, targets, locations, aircraft numbers and squadrons etc. Look for an existing mission similar in nature to the one you are trying to create eg large or small intercept, ground attack, convoy attack. Most mission types already exist and can just be copied and modified to taste. Elements of some existing IA missions are 'hard coded' in though - no matter what you change in the mission editor, it won't change in the game.
3. As soon as you are happy with a new mission, make a backup of the quick.dat file (this is where the mission data is stored). This is essential because the next time you fool around with a mission, you can corrupt the quick.dat file and you may lose all the work you have already done! The mission editor program is unstable, and crashes frequently.
4. I mean it!
Back up the quick.dat file every time you are happy with your changes, or you WILL lose them!
5. If you don't like a mission you have created, you can delete it, but you have to 'save/recompile' the quick.dat file or it will still be there when you load it up next time.
6. Most common time wasting error I made was to start editing an existing IA mission, rather than copying it first! Doing this wipes out your existing IA mission and the only way to get it back, is from the backup quick.dat you most recently made. You did make that backup, didn't you?
7. Sometimes the mission builder will do something quirky which you can use to your advantage, so think creatively. For example in my Aces Mission pack I assigned a flight of Blenheims with Hurricanes to escort them. I had a vague idea I might be able to get them to bomb a Luftwaffe base and I could actually build a mission where the RAF escorts an attack on a German target in France or Holland. But the game assigned the Blenheims to the German side and instead of escorting them, the Hurricanes started attacking them...this turned out to be a boon because it reflected an unfortunate incident in 1940 of 'friendly fire' by 1C Squadron where exactly this scenario really happened. Voila, a surprising and interesting mission was born!