OBNB doesn't sell books, but you may be able to find a copy at one of these websites:
Exhibition of English drawings, watercolours and paintings : [catalogue of an exhibition held at] P. & D. Colnaghi & Co. Ltd ... 14th November to 7th December 1973 by P. & D. Colnaghi & Co.. ISBN 0904221008. Published by P. and D. Colnaghi and Co. Ltd in 1973. Publication and catalogue information, links to buy online and reader comments.
![Exhibition of English drawings, watercolours and paintings : [catalogue of an exhibition held at] P. & D. Colnaghi & Co. Ltd ... 14th November to 7th December 1973](http://ecx.images-amazon.com/images/I/41RhvMJ6ilL._SL160_.jpg)