Or try a health food store. If you've got a halfway decent health food store that sells miso and au naturel tamari and other kinds of seaweed and so on, chances are good that they'll either stock nori, or be able to order it for you. I can't get it in the (pathetic) Asian food stores here in my small Ontario town, but do see it at my local organic store.
(I prefer, however, to drive into Toronto, go to Japantown, and buy the huge cowchoking packages of the really good stuff...)