http://www.irish-sayings.com/
hope this website helps, if you register you can get the phrase you want, otherwise, I have double checked this for you but I am not sure how it's pronounced (I'm Scottish!).....
go raibh maith agat (when talking to one person)
go raibh maith agaibh (when talking to more than one person)
fee
p.s The scottish Gaelic way is
tapadh leibh (when talking to one person)
tapadh leat (when talking to more than one)