BUYING THE VOCAL SCORE
If you would like to buy a Vocal Score (all the singing parts with piano accompaniment) before the rehearsal weekend then there are several music websites from which you can order a copy. There are many editions of the Messiah but one of the most usable is the 'Watkins Shaw' edition published by Novello.
www.musicroom.com
www.sheetmusicplus.com
www.amazon.co.uk
There's also a set of books especially created with CDs for the purpose of "Scratch" Messiah performances. See below for websites from which you can learn your individual part.
Messiah from Scratch
Published by Faber
Messiah from Scratch
Published by Faber
Available in Soprano, Alto, Tenor and Bass.
LEARNING THE MUSIC AT HOME
There are lots of websites now from which you will be able to download parts for your own private rehearsal at home. Some of these have the accompaniment with the chosen chorus line played noticeably on the piano.
http://savedsounds.com/Messiah/Messiah_parts_mp3/index.html
http://note-perfect.com/index.php?main_page=index&cPath=7_36_40