If you are interested in purchasing official merchandises of Tokyo 2020, summer Olympic games in Tokyo this summer, there is an official online store in English but unfortunately they do not ship to overseas!
In case you have a friend in Japan, ask the store to send the products to your friend's home and ask your friend to ship to your home or keep them at your friend's house and pick them up later when you visited Japan.
Please be aware when you buy clothing, for example T-shirt. The size is for Japanese and Japanese XL is European M or may be smaller!