This requires a relatively recent version of cctbx (some bits of xia2 were moved into cctbx.)
Select "show unreleased builds"; select *green* link like YEAR_MO_DY_NNNN (e.,g. 2013_05_07_0005 today) then download the appropriate build for your machine.
This should be automated as part of a xia2 download script: I will look into it. Please be sure to source the cctbx setup file after CCP4 as CCP4 distribute an old version...
Problems / questions to the usual place: email@example.com