It may be available through one of the "print-on-demand" services - I've bought books on that basis from both Waterstones and Amazon I think. I'm just looking at a book by Wolgand Iser published in paperback in the US, but it says at the bottom of the back page that it was actually printed in Milton Keynes on 4 March 2010 - in response to my order for it. Because of the cover prices of academic books it makes it worthwhile to do it. I think one of the Blackwell stores in London has a walk-in service for print-on-demand.
Of course, there might be a completely different explanation in your case
