Irish Rugby Supporters Club members will receive a priority ticketing option before tickets go on general sale. Some tickets have also started to appear on the secondary ticket market, on sites like Viagogo.co.uk and GETMEIN.com.
Usually season ticket holders of the irish clubs get first pick of the seat tickets. After that tickets are allocated on a first come first served basis. There'll be plenty left, usually just over half are left on sale. Youre best off giving the IRFU a quick ring to be ahead of the game, as the rest of the tickets would go in a day id imagine with other fans wanting tickets.