Mount Fuji is a very representative landmark in Japan, so you can buy various souvenirs with the theme of Mount Fuji, including Mount Fuji Cup, in specialty shops or souvenir shops around Mount Fuji in Tokyo. These shops are all over the business district of Tokyo. There are shopping malls and shops in Ginza, Shinjuku and Shibuya, which are very convenient. You can go shopping in these places.
Besides specialty stores and souvenir shops, you can also go shopping in Japanese department stores. In department stores, you can find Japanese specialties, including Mount Fuji Cup. In the process of buying, you can choose to buy goods with price tags, or you can choose to choose goods in the store and then ask the clerk for the specific price.
In short, it is not difficult to buy Fuji Cup in Tokyo. You can go to specialty shops or souvenir shops around Mount Fuji, or you can go to department stores to buy them. In the process of buying, you can know the price of the goods first, and then choose to buy.