I own a complete N64DD game collection. Kyojin no Doshin: Kaihou Sensen Chibikko Chikko Daishuugou and Japan Pro Golf Tour 64 are the two rarest games for the system, from what I understand Kyojin no Doshin: Kaihou Sensen Chibikko Chikko Daishuugou was mail order only.
I was lucky to find the two rarest games at a game store in Denver for $400 for the pair.
