Do you have to go to Japan to find them? How much do they usually cost?
I think "most" of them have turned up through Japanese auction sites and other Japanese sources - after all they were only ever sold and for a very limited time in Japan. So you maybe dont have to go to Japan but for those not currently in the hands of collectors I would guess if and when they show up its most likely they ll be in Japan.
I dont know how much recently they have changed hands for because they would have been personal transactions but I would guess on the open market on ebay you would be $1000 plus region and goodness knows how much more for MIB items