Hi, Ned -
I found a recording on Spotify of a performance of "Ellan Vannin (Dear Isle of Man)," performed by the Glasgow Orpheus Choir under the direction of Sir Hugh Roberton (of Mingulay Boat Song fame). Also another by the Seven Towers Choir. I suppose, however, that you're seeking a choral arrangement on sheet music.

Not a full arrangement, but this (click) may help you.

Oh, and since you're in the UK, it looks like you can buy a choral arrangement through Amacon:

http://www.amazon.co.uk/F-H-Townend-Ellan-Vannin-Sheet/dp/B00CWEDJQY

-Joe Offer, Mudcat Music Editor-
(email sent)