Where can I find great Japanese waterstones for knife sharpening?

My boyfriend and I are both culinary students and total foodies. He works in the industry full time and he goes to school full time. His birthday is coming up and I really wanted to get him some stones for sharpening. I have only ever used oil stones so those are all I am familiar with... but he tells me all of the time that he likes Japanese waterstones much more, so I'd like to get him some. I have no expirience with them so I don't know what to look for (or if they're all the same) and where I could buy a good set.