The limited edition flavors are sometimes available outside of their "jurisdiction." Some convenience stores have random theme sales (Okinawa and Hokkaido are popular), also you may want to check out prefectural
antenna shops to see what they have in stock. Generic souvenir stores (ie, in major train stations) can come in handy.
Last edited by BuildingMyBento; Apr 28, 2013 at 10:21 pm
Reason: added link for English explanation of antenna shops