OBNB doesn't sell books, but you may be able to find a copy at one of these websites:
Alan : casgliad o gerddi ac ysgrifau ar Alan Llwyd, gyda llyfryddiaeth lawn o'i waith gan Huw Walters. ISBN 1900437511. Published by Barddas in 2003. Publication and catalogue information, links to buy online and reader comments.