Considering it will probably be a while (if ever) before we get the chance to listen to a proper Mega Man Legends 3 soundtrack, Hypershell has taken it upon himself to piece together one of the themes from the Nico Video gameplay of the game's footage. Check it out:
Of course, even if the game does see an eventual release, that doesn't necessarily mean that this theme would be a part of it. As least we can still enjoy it as a neat theme on its own. And if you're interested in downloading an MP3 version, you're all set, with Hypershell adding "I encourage ANY fan to reuse this as they see fit."
Source: Protodude's Rockman Corner