Call Irish Rail on 01 703 1884,
europeanrail@irishrail.ie, or visit Dublin Connolly, Cork, Limerick, Waterford, Sligo or Galway stations, there are others as well
Call Stena Line on 01 204 7777 quoting 'rail' or visit them in Dún Laoghaire
Call Irish Ferries on 0818 300 400 or
sailrailirl@irishferries.com
Failing that Ryanair/Aer Lingus/Aer Arann/Fly Be/BMI/BA will get you there at least 6 hours faster. Birmingham is generally the best option (quiet airport, train station, rail ticket collection machine in the baggage collection hall) with either Ryanair or Aer Lingus, can get direct trains to most places from the airport or after a short trip to Birmingham New Street, or same thing to Manchester/Gatwick/Stanstead/Heathrow book with trainline.com which will accept Irish addresses and has favorable reports on this forum
Of course it would be lovely to get the TVM system to be able to handle these tickets but in reality there are major problems with routine tickets currently which need fixing, trouble enough getting a few miles down the road let alone half way across the Irish Sea.