As far as I understand you can only buy them at his seminars. He said at the seminar this spring that he only sells them at the seminars sort of as cliff notes on what they have experienced with him directly.
Ikeda Sensei's stated reason for this is that what he is doing looks fake. He didn't want to put his videos out there to folks who hadn't first "felt it". I have certainly had that experience myself with some video clips I posted. The folks who have never trained with me often thought my ukes were colluding, the folks that had actually been on the mat with me knew I could do what I was showing.
There's enough BS around that I think he wants to be careful of his reputation. I'm not sure why he cares really... he teaches world wide and constantly, there are quite enough folks out there who get to work with him in person that I can't see how a few doubting Thomas's would hurt him. But that's why he doesn't sell the videos outside his personal appearances.