May not be the original video, but it's a good one nonetheless.
http://www.youtube.com/watch?v=3cyHsZmM-eo
Where you can download the MP3, or the whole album. Comes with cover art that you can use.
http://acousticbrony.bandcamp.com/
Lyrics are right here:
http://acousticbrony.bandcamp.com/track/loyalty-acoustic-version
Requesting the acoustic version specifically.