I currently fly missions in the FSX@War P3D compatible version 1.2.3. I believe that is the last version before the team broke up that was developing it. Great piece of software. There is a pack you will have to install, do a google search on this "FSX@War SEA 1.2.7". You will have to add it to the P3D Scenery and you will have to have FSX@War running to see the scenery. It's not a completely finished theater though. I was in the process of trying to covert the old FSX Vietnam War project, but when FSX@War came out with that theater I stopped work on it.
Hope this helps.
Edit: forgot to mention I hope that the scenery guru's here would look into finishing that theater and create some other scenery, like North Korea, Iraq/DESERT STORM, etc. I'm currently (when I have a few moments or take a break from writing code) working on an NTTR theater. If ever get it finished I'll create an install pack and release it.