Since the official OST doesn't exist I guess you asking for a game rip.
Well if you don't care much for perfect audio quality, then check here: X Men Legends 2 - Original Game Audio MP3 Downloads (
http://gh.ffshrine.org/soundtracks/1059)
If you do care about quality, then stop by VGM Legacy thread and make a rip request when those guys have available requests left.