No doubt the Roy Palmer edition is great, as are his other many books. However I found the original Version here , along with many other complete books, songs etc.
I assume they are all out of original copywrite.
I really only did the search to see what was available, as I am performing one of the Hereford Carols(#8 above) this Christmas. I got my version from a Lucy Broadwood collection, which I purchased last year from Mudcat Auction.
JohnB.