OBNB doesn't sell books, but you may be able to find a copy at one of these websites:
Ar maidin moch : pacáiste sraitheanna le béim ar bhriathra na Gaelige by Nóirín Ní Nuadháin. ISBN 190556001x. Published by Cló lar-Chonnachta in 2006. Publication and catalogue information, links to buy online and reader comments.