If you can find a copy of An Pósadh: Treoracha: Léachtaí: Guí an Phobail published by An Sagart, you may find the prayer you are looking for.
The Paróiste Naomh Muire – Dingle Parish Online website has the Guí an Phobail for a funeral service, but not a wedding service. Still an interesting resource: http://naomhmuire.wordpress.com/resources/funeral-readings-gaeilge/.
Ádh mór ort!