Question Where can I buy 13x8 passive bass driver?

Does anyone have any ideas where I can buy replacement passive bass drivers (13 x 8) for a 70s/80s quality loudspeaker? Originals have succumbed to sun exposure. Sorry at moment I have lost paper with make and model number of speakers - all other drivers look and sound good and I would like to repair these for a friend

 

At a guess that sounds like a Kef B139 passive radiator.
http://kef.com/uploads/files/en/kef_units/A History of Kef Drive Units issue 3.pdf
Scroll down a few pages for the details. Chances of finding some are slim as Kef do not make them any more but there is this site http://www.retrotechaudio.co.uk/classic-kef-spares.html