japan has a lot of unique flavours of kitkat and it only available in Japan. Some of them can only be found in a specific area which means it is a really a mush have item because it can't be found in another places.
i have taste a view flavour when i went to japan last july. the easiest flavour to find is ice cream and dark chocolate. you can get in almost every kombini (convenience store). we can find it at the airport to but only a few flavour such as hotcake, greentea, strawberry, sakura mochi, and kuromitsu.
the price is about 180-1500 yen.