Re:
They did rear ones too. It bolted on to where the roller was threaded on to. Worked a treat and really improved the braking. You could also get one designed to fit through a brake booster which stiffens up the rear too.
As I use vs now, I run a booster with them, about to fit some avid black ops to replace the xtr vs, but the xtr brakes with xtr carbon booster are a really good combo, though fiddly to adjust the brakes as you can't access the cable bolt with the booster in the way, so have to set up the brakes without it, then fit the booster.