You don't say whether you mean Northern Ireland or Eire
For NI the most up to date information can be found here
https://www.groni.gov.uk/aboutus.asp
They do not offer a comprehensive list of venues but say the local district registrars will know.
http://www.groni.gov.uk/contacts.asp
You could also try emailing the central office
groreg.nisra@dfpni.gov.uk
For Eire we don't have so much info but you could try at
www.weddingsonline.ie which is the biggest Irish wedding site.