If you can`t find it you have to ask yourself how badly you want to play the game.
I think it's possible to edit all the missions so as to not need CD2 anymore. If you're good with Fred it won`t even take you very long.
First try to install the game. Do a minimum install. The installer will cry at the end of the installation when it tries to play the Descent3 demo but it should have installed FS2.
Test this by trying to play the game with disk3 in the drive. It should work but will ask for disk2 when you try to enter the mission briefing. Quit out of the game.
All you need to do is remove all the cutscenes from in the campaign editor. That should take you about 5 minutes maximum.
Next you'll need to open the individual missions in Fred and edit out the references to the command briefing ani's. That should take you about 2 minutes per mission.
Insert CD3 and start the game. With luck FS2 won't ask for CD2.
Of course I`m assuming you have some experience with FRED2 and already have a copy of VPView to extract the campaign file and the mission files. If not the link at the bottom will take you to my FAQ which will help you with those.
My advice. Try to find (or buy another copy of) the CD. You`re missing a lot of good stuff without it. Failing that try to play the first mission using my advice. If it works you can edit the rest of the missions which need CD2.
Let me know if it works BTW.
Edit: Just noticed that according to Vader CD2 also contains the music data. Opps. I don`t think the above will work unless you`re willing to edit the music table too.
