For performances of 18 Musicians checkout the Boosey and Hawkes page: http://www.boosey.com/pages/cr/calendar/perf_results.asp?pg=3&composerid=2781 or from the official Steve Reich site http://www.stevereich.com/concerts.html
If you know of any others then let me know!
Music for 18 Musicians - Score from Boosey and Hawkes
According to the notes in this book it took Marc Mellits, a composer in his own right, to perform a Doctoral Dissertation on Music for 18 Musicians to actually get the piece onto manuscript. Up to then it had resided really only on bits of paper and in the heads of the performers in "Steve Reich and Musicians". So the only group to perform it was Reichs own group all the way from its first performance 1976 to 1997. Once Marc Mellits had performed his dissertation it left the score open for other performers to take the piece and perform it and also record it. Thus we've had three renditions outside of Reich's own group which are discussed in Available Recordings.
Of course much of the score consists of repeats of previous bars but it is fascinating to see the notes on a stave and indeed if you feel inclined play some of the elements along with the music Much thanks must go to Marc Mellits over the huge task that he undertook. If it wasn't for him we may well not have a score at all and we'd still have to wait for Steve Reich to come to town to hear live this most wonderful piece of music. Marc said "It was an absolute joy. It took 2 years to do and I never grew tired of the process. I loved working on it."
This version is one of Boosey and Hawkes "Pocket Scores". The book can be obtained direct from Boosey and Hawkes here price as of December 2009 is £36.99
"Writings on Music" - by Steve Reich
This book is only really of interest by someone who is already a fan of Steve Reich or potentially someone who is a student studying the composer. It consists of various writings and interviews by and with Steve Reich and runs in a timeline from 1965 through to 2002 (just up to Three Tales). 18 musicians is mentioned although the main feature on it quite well known, versions of it being found in lots of places including the back of the original ECM recording. He does however discuss the process of the composition in an interview with Michael Nyman (no less). The paperback version of the book as of 2009 is found here at £12.28
More Information from the Internet
Steve Reich's Official Site. Not updated very regularly but a good source for future concert information across the world. It includes an 12 minute recording in MP3 format of the opening of the World premier of 18 Musicians 24.04.76.
Mostly Japanese - link to Composium 2008 featuring Steve Reich and Music for 18 Musicians (thanks to Daniel-Sascha Roth) . Also here you can see a complete Video of the event from Composium 2008 in Japan with Steve Reich, Ensemble Modern and Synegy Vocals. This includes an Music for 18 Musicians, Daniel Variations and a fantastic studio presentation of Different Trains. You need to download the Veoh viewer and possibly some extra video codecs. Some of this is also available in smaller junks here on youtube.
The Nonesuch page on Steve Reich with a neat biography, news of new recordings and also a way of sampling the delights of their rendition of 18 Musicians (thanks to Daniel-Sascha Roth)