Thank you both for your interesting replies. I haven't asked at the MNHL about their photo collections as we both remember such a picture and my daughter has never been in there. We feel it must be publicly available somewhere, though have come to the conclusion it must have been in a display somewhere like the Manx Museum, House of Manannan or even Rushen Abbey. Not to worry - we'll probably come across it again years from now and wonder why we ever wanted to know!

Thanks again for taking up the cause.