im from ireland and started my jumping here
the biggest dz in the republic is the irish parachute club and that is probably the website you found http://www.skydive.ie/ the other dz in the republic is called skydive ireland http://www.skydiveireland.ie/
they are a far newer dropzone but its were i started jumping and i like it everyone is really friendly and imsure they would love to get some travelling jumpers up there, it is about 2 hours from dublin. iv never jumped at the ipc and im not sure how far from dublin it is it could be around the same.
i dont think either of these dzs are open full time but open friday saturday sunday, the ipc might be open thursdays too
the other dz in ireland is in northern ireland called the wild geese iv never jumped there but if you google it you should get their website