They're not hard to get in the Kansai area but I don't know about Tokyo.
Actually, I'll be in the Tokyo area around the end of March, too. I'll be there from the 22nd through the 25th, returning to Osaka on the evening of the 25th. If you're around, have time and are inclined to make the pilgrimmage to the Tezuka museum I'll happily show you how to get there, but is it several hours away and the bullet train is a little expensive for a one-day trip.
If you see a Comme Ca store around, they usually sell Tezuka Moderno stuff! Also, I found this place through a Google search:
http://tokyoq.com/weekly_updates/tqoole/atom.html
I'm not sure how recent the article is, though; I remember hearing about a Tezuka store in Tokyo that closed down.