Laura,

There are a number of Arthurian cognates in legends of many regions of Europe and the Mediterranean, some as far away as India. Adonis, Attis, Osiris are three who get mention in scholarly works by James Frazer and Jessie Weston. The stories of Parzival/Parsival/Parsifal (also called Perceval, other variants are Percyvelle and Perlesvaus--this last one yeilds some good and very old information, I think) all contributed to or benefitted from the legend of Arthur and the Green Knight and the Holy Grail. You may recognize the name Parsifal because of Wagner's opera. These are all popular and related stories.

There is lots of old poetry that can be adapted to song, and probably songs transcribed as poetry in the many books referred to in Weston's wonderful little book From Ritual to Romance.

Arthur is a spinoff of a fertility legend, as are the others. The waters, the wasteland, the grail are all part of that. There is tons of stuff if you do some searches, but I wouldn't suggest Google for this, though you'll possibly scratch the surface. I suggest you go to a large library with books or large online fee (scholarly) databases where you can search on some of these terms. Find the OLD version of The Golden Bough (the one that is in many volumes). And find a copy of Jessie Weston's From Ritual to Romance. I just thumbed through it and found many exerpts from Medieval poetry. If you look up her book on The Green Knight I think you'll find even more. She quotes a lot of Mallory, though she also disagrees with many of his conclusions. I am in passing familiar with the Green Knight book, but haven't read it. I think it contains a lot of material in poetical form.

In addition to Frazer and Weston, James Campbell has written about the Arthurian legend and no doubt has an extensive bibliography. There are many scholars more modern than these three, some who have put slightly different readings on the primary materials in question. My work with this was in English Lit where I was working with early 20th century authors, so I wasn't pursing the more modern scholarship, but it's out there.

I hope this helps.

SRS