OBNB doesn't sell books, but you may be able to find a copy at one of these websites:
Gaoth an fhocail : foclóir analógach by Breandán Ó Doibhlin. ISBN 0862890748. Published by Sáirséal Ó Marcaigh agus Coiscéim in 1998. Publication and catalogue information, links to buy online and reader comments.