Nah, I looked and it's not there. Unless it's in that Descent 3 shippack, but I think that's the Pyro-GL, not the GX.
Also, I forgot I had my back-up HD with me. And what do you know, the Pyro's sitting right there!
So I went ahead and uploaded it to FSmods. It won't actually be up for download until an admin reviews the file, but give it a bit of time.
Anyway, since I'm not on my FS-playing computer, I have NO way of knowing if this is totally compatible with modern FS_Open releases. Just FYI.