DFB recently posted a video on
YouTube about Tokyo
Disneyland and things to know before a trip. They mentioned for certain times of the year you can only book 3 months in advance and for some, 4 months. And that you have to be online and ready to go exactly when rooms get released (around 10pm EST - they tell you the exact time, I don't remember), also advised not to spend time looking at different rooms and categories because by the time you are done, the rooms are booked. It could be your timing or that the rooms are gone. Good luck, it looks like an amazing place to visit!