You can use my binstar channel which should have linux64 binaries:
conda install -c nbren12 iris
Or clone this repo and build manually using conda build.
Afterwards, if libudunits2.so is not installed systemwide, you will need to tell it where to find its XML file. You can do this using an environmental variable export UDUNITS2_XML_PATH=<PREFIX>/share/udunits/udunits2.xml