The House of Edgar line of Irish County tartans were created by Polly Wittering in 1996. All are available in the 13 oz. range (Irish National is also available in 17 oz. Heavyweight) and have proven very popular due to their wonderful palette of colours.
It should be be noted that, at present, none of these tartans have any official standing with the governmental bodies of the regions which they represent. The six counties which make up Northern Ireland (Antrim, Armagh, Derry/Londonderry, Down, Fermanagh, and Tyrone) no longer have official status. Many Irish kilt wearers choose a county (or provincial in the case of Ulster) tartan to represent the county they or their ancestors hailed from.
Here is a link to the Irish-themed tartans (and their respective ranges) offered by the House of Edgar: