Although this might not with the answer the OP wants, I'll just chip in my 2 yen for anybody who finds them useful:
A search on the Web showed no graded readers in Japanese (maybe they're found only when you sweep through all the bookstores in Jimbo-cho). So, the second-best alternative I can think of is going for Japanese version of classical works from around the world:
少年少女世界文学全集 (shounen-shoujo sekai bungaku zenshu)
They can be bought separately. You can pick a book you've already read as a kid and read it in Japanese. (These versions usually are simplified and have furigana for the relatively difficult, if not all, kanji.) These collections also include works by Japanese authors.
If you feel comfortable with these, there are Japanese digital libraries, offering access to some books (not in text but in graphics):
International Library of Children's Literature:
http://kodomo4.kodomo.go.jp/web/ippangz/html/TOP.html
National Diet Library archives:
PORTA統合のお知らせ
Hope it helps even a little!
PS: I forgot to add that this current bestseller is being recommended for Japanese language learners (intermediate or better) who want to read something that doesn't insult their intelligence!
(Written in plain Japanese about economics at work in everyday living):
さおだけ屋はなぜ潰れないのか? 身近な疑問からはじめる会計学 (光文社新書) | 山田 真哉 |本 | 通販 | Amazon