There's actually some stuff on the internet about them.

The group's founder, John Pac, passed away in 2013 after founding a record label, Kingsway Music

http://parchmentmusic.blogspot.com/

https://www.youtube.com/playlist?list=PLA7C3C3E1CDC30A56

http://www.crossrhythms.co.uk/artists/Parchment/7552/

http://worldwide-christian-ministry.org/parchment-light-up-the-fire-1972-gbr/