Update! Below is an email sent to Waterstones followed by their reply. Looks encouraging, but I'm not holding my breath!
"Thank you for your email and for chasing this matter.
My query is this:
Do the suppliers KNOW that they can fulfill the order since, as I mentioned on the phone, I have heard through a third party that the author, Russell More, has no copies and that the book has sold out.
I'm happy to wait if they can answer my question in the affirmative. But I do need it for Christmas".
"Thank you for contacting us. I apologise for the delayed response.
They have been us that they can do this but that this will take another 2-3 weeks just because of the delay.
I apologise for the inconvenience" .