OBNB doesn't sell books, but you may be able to find a copy at one of these websites:
Józef Piłsudski : Komendant _ Naczelnik Państwa, pierwszy Marszałek Polski by Juliusz L. Englert. ISBN 0850652200. Published by Polska Fundacja Kulturalna in 1991. Publication and catalogue information, links to buy online and reader comments.