Donna Burke has published some of the Metal Gear Solid Vocal Tracks on her Youtube channel. These songs can be found on a soundtrack CD released alongside Metal Gear Solid V: The Phantom Pain in Japan.
Those living outside Japan can order the CD from CD Japan, for around €22 excluding shipping: Purchase from CD Japan (Affiliate Link)
For more info on this CD, as well as the other MGSV Soundtrack CD, go here.
Source: Donna Burke Youtube