I don't know if there are already topics about Japanese gardens. (Have you checked that yourself?). Maybe this book can be helpfull:
Amazon.com: Japanese Gardens (Taschen 25th Anniversary): Books: Gunter Nitschke
A simple search on Google will give you lots of pictures also.
I very much liked the rock garden of the Kongobu-ji in Koyasan. And the Korakuen Gardens in Okayama could also give you some inspiration?
I hope this helps a bit.