In Southern Ontario, I've never seen it.
amazon carries it, the shipping was like $20 before so i'd get it while the shipping is free
http://www.amazon.com/Irn-Bru-Case-Ounce-Bottles-Shipping/dp/B003KPLWKE/ref=sr_1_2?s=grocery&ie=UTF8&qid=1396533514&sr=1-2&keywords=irn+bru
Ireland and yes it is reasonably common in the shops especially in Dublin. Tasty stuff. It is one of my go to if the shop does not have Jones or Root Beer.
Down in Australia I see it from time to time at supermarkets, more often the speciality ones but occasionally Coles, and of course at the sweet shops.
I can occasionally get it here in Indiana. Get it from some family friends, they're Scottish, and I'm not entirely sure where they get it from but I remember them saying its from somewhere near here.