Originally published: New York : Dial, 1975 ; Harmondsworth : Kestrel, 1977.
OBNB doesn't sell books, but you may be able to find a copy at one of these websites:
Morris's disappearing bag : a Christmas story by Rosemary Wells. ISBN 0140503196. Published by Puffin in 1980. Publication and catalogue information, links to buy online and reader comments.
