I know KitKat maccha flavor is popular souvenir for foreign tourist, this year Nestle Japan released KitKat Sake flavor! This is sold in souvenir shop in airports. Not only maccha and sake, there are more unique Japanese flavor of KitKat.
Here is local KitKat map. You can buy those each area's big souvenir shop.
KitKat Purple Potato from Okinawa, KitKat Wasabi from Shizuoka, KitKat Houji tea from Kyoto.
In Past, we have strange flavore like this. Japanese like sweet beans very much. KitKat Sweet Edmame, KitKat Soybean Power, KitKat Sweet red bean.