There are loads of Vaughan Williams arrangements of folk songs for choirs - very good in general. Cecil Sharp also did some, but the VW are really the favourites.

There may be sheet music on the web, but it's not too difficult to find in the secondhand bookshops. There may well be some new books available in music shops too.

I've got a dozen or so scored arrangements somewhere if that would be helpful.

Cheers!
Ian