Sourcing Cloud 9 underlay locally

We're considering buying a carpet from Carpetright (on a fairly tight budget) but they stick the arm in when it comes to all the extras like underlay so we plan to keep costs down by sourcing everything else ourselves. I believe that Cloud 9 underlay is pretty good and much better value than the underlay that the big carpet sheds sell.

Does anyone know where I might be able to get Cloud 9 underlay locally (we're in Belfast)?