ID and sport horse biggest venues are Cavan and Goresbridge - google both for websites. Tattersalls for TB at Fairyhouse. All are advertised in H&H fairly regularly. Most of them offer incentives to buyers from the UK. Hope this helps.
Don't expect Cavan or Goresbridge to be full of bargains, though... So many more people go over than, say, 5 years ago and most know a good horse when they see one!