By site editor Dan Chung:
At Inter BEE 2013 I spoke with bespoke Japanese lens and rig workshop Technical Farm. They offer a range of Canon L zooms converted for Cine use with the addition of hard stops to the focus mechanism and a smooth manual aperture ring. They currently offer conversions for the 16-35 f2.8L II, 24-70 f2.8L (first version) and 70-200 f2.8L II.
They also make rigs and custom support gear. You can see more on their website (in japanese).