OBNB doesn't sell books, but you may be able to find a copy at one of these websites:
Emynau'r ffydd : 100 myfyrdod ar rai o emynau enwocaf Cymru by Huw Powell-Davies. ISBN 1859944957. Published by Cyhoeddiadau'r Gair in 2004. Publication and catalogue information, links to buy online and reader comments.