If the tiles are that recent, it would undoubtedly be worthwhile checking as many B&Q stores as you can, as some may well still have old stock.
Maybe you could enlist the help of other users of this ng - people have certainly done so in the past - that way you could potentially cover every B&Q in the country! Although I appreciate it might be awkward if you're just looking for an 'old' batch of a current design (if I understand correctly?)
David