The Kell Hounds scenario pack/sourcebook describes the Eire BattleMech Company of Arc-Royal as producing "spare parts, but no fully functional production models at this time." circa 3029. Handbook: House Steiner's profile of Arc-Royal MechWorks (circa 3067) notes that it was previously the Eire BattleMech Company of Arc-Royal, a minor manufacturer of 'Mech parts.
However, in "Vanish," (3005) Morgan Kell recounts having grown up on Arc-Royal watching BattleMechs walking off the factory floor, and in "Not the Way the Smart Money Bets" (3010) Mr. Franck from the Lyran office of Mercenary Relations tells the Kell brothers that Eire's products are "rather important to the defense of the nation."
So, what did Eire make other than spare parts, and when/why did it stop making BattleMechs? The writeup says that Combine raids were rare, due to the distance from the border, but that there was a violent clash between Buddhists and Catholics on Arc-Royal in 3026 that required the intervention of the Commonwealth Religious Council. Was Eire a casualty of religious strife?