There's a great feature about the soundtrack on the 40th anniversary blu Ray. The John Phillips soundtrack features some of greatest uk session musicians of the time (Herbie Flowers, Big Jim Sullivan, Mick Taylor from the Stones) but even more intriguing is the fact that Bowie created the first soundtrack which was never used and is probably lost (except for an unnamed track appearing on "Low").
John Philips also played a role in selecting the non-original music (Roy Orbison, Holst, Louis Armstrong, Yamashita, the Kingston Trio) which is eclectic and perfectly suited to the moods.

OMG thanks so much for that. At last!!!! I've waited 40 years for a soundtrack album. So much interesting music in that film. Cant wait to hear it all.
The Octave Doctor

Indeed, the soundtrack is out this week in the UK.
The track you are referring to is called 'Alberto', track 07 on the 2nd CD.

You might be able to find out when the soundtrack is released in September!