According to the Wikipedia article for "The Great Wave off Kanagawa", copies are stored in various places around the world.
There are various copies of this work throughout the world. The Metropolitan Museum of Art in New York, the British Museum in London,1 the collection of Claude Monet in Giverny, France, the Sackler Gallery, the Guimet Museum and the National Library of France are some of the places where this work is on exposition. A collection of woodblock Thirty-six Views of Mount Fuji prints, contained in the wellness spa of the Costa Concordia was lost during the collision of the ship on January 13, 2012.
Some private collections also have a copy, as is the case of the Gale collection in the USA.
This article (accessed May 14 2014) does not list one place I would expect - Japan! Is it possible to view this woodcut in Japan, or are all of the copies overseas?
edit: See answers below but there is an idea that there is no "original" because it's a woodcut, the same way there is no "original" of a photograph because you can print many copies from a negative.