Hi Geoff,
Yes I've seen this in the book and I have a collection of these WWI poetry postcards but mine all allude to army camps and the trenches. There is a good chance some may have survived. Have you tried all of the following? Postcard sellers online, Ebay.(Zeppelin), the exhibition down Whitefriargate, the people who put on the WWI exhibition at the Ferens recently( Susie Capes at Hull Museums)?

Thanks for coming to the concert on Saturday. Sorry I didn't get to chat with you both.

Steve