OBNB doesn't sell books, but you may be able to find a copy at one of these websites:
James Fitton, R.A. 1899-1982 : Dulwich Picture Gallery 12 November 1986-4 January 1987 by John Sheeran. ISBN 0950156426. Published by Dulwich Picture Gallery in 1986. Publication and catalogue information, links to buy online and reader comments.