Kefdirect.com is a good source , sometimes accessories4less.com will have a pair if you google you maybe be able to get a pair on a discount if you can wait until November most dealers have black friday deals
or you can join the kef group on Facebook and see if someone will sell you a unit. you can also look at a cheaper option audioengine HD6 they are fabulous speakers for the price I have all 3 !

I use the Passive LS 50 for my HT front speakers , LS50W in my homeOffice Desk Top speakers and AudioEngine HD 6 in my bedroom with a 50 " Oled 3D TV
Asghar