Firstly, there is Stirton.com, a forum run for UK and Irish ISSF target shooters. There are specific sections there for discussing Irish competitions and the NTSA.
Secondly, there is the Shooting Forum on boards.ie, a forum which is dedicated to Irish shooters of all varieties, including NTSA, NSAI and NASRC shooters; as well as hunters, shotgun shooters, and firearms dealers. This isn't run by the NTSA, but does discuss NTSA shooting.
Thirdly, there is TargetTalk, a forum mostly for US shooters, but as it has some of the most well-known shooters in the world posting there (such as Matt Emmons and others), it's worth the perusal.