Hi there
There are quite a lot of good sites up around there. Here are the ones I've been to on OS sheet 24* :
http://www.megalithomania.com/show/sheet/24
This one is in Ballina (and signposted) up above the train depot:
http://www.megalithomania.com/show/site/667
So, if you use this page you will see what's close to Ballina:
http://www.megalithomania.com/show/nearest/site/667
A lovely part of the world up there. Enjoy!
*I strongly recommend you buy this and any other OS maps you might need for your trip.