Update 6.5.2011: Please see the comments. This branch may have moved.
A word in your shell like ... the Shinanoya store in Roppongi had a few bottles of Plum Liqueur Cask Finish when I looked in there last week. I had heard it was supposed to be distributed only to bars. Perhaps that was just the initial release? Anyway, the price is just short of 10,000 yen. Personally, I think it is a steal but I can't afford it.
The store has a limited but quite interesting Japanese whisky selection. The Shinanoya stores in general are worth popping into if you are looking for the good stuff. Here is a map of their locations. This is the page for the Roppongi store. Here is the Shinanoya website and here is their Rakuten online shop.
I have put the Roppongi store on my map of whisky outlets in Japan and will try to add the others when I have a moment.
Address in Japanese