Japanese regulations on keeping reptiles is different for each prefecture. As far as I remember, You need governor's allowance to have several big Boas and pythons or venum snakes in "Kanagawa" pref. Consult prefecture office. There was a shop "Pinky & Killer's" which mainly treats snkes in yokohama. I don't know this shop is still open. In Tokyo, there are some good shops. "Hachurui-Club", "Max Reptiles", "Woma", ect.