The info you're looking for is on the web, well a lot of it is.
O'Hara's export 75% of their output (a portion of which is not own-label), turnover is around €21 million. Porterhouse export around 5%. Turnover around €32, but a lot of that is not brewing related.
No-one else is exporting I think, but I believe the Franciscan Well are looking to start.
In the time immediately prior to 2004, only O'Hara's was exporting I think, and you'd have a bit of a trawl to find what the figures were.
Company accounts are publicly filed, and are another place to look for info.