Yes, you can find events and sign up in English
Participation of foreigners in sports events in Japan has been increasing in number, especially in international marathon races such as "Tokyo Marathon". On the other hand, it is still not easy for foreigners to find local sports events held in Japan as well as to sign up for participation as event information and the entry form are usually available only in Japanese.
SPORTS ENTRY now provides information in English (partially in Chinese) and allows users to find and register various sports events in Japan, including marathons and bicycle races. The registration can be made in English
The number of events are not many yet (as of Feb 2017), however, they are planning to add more selective events and expand their services.
SPORTS ENTRY (English)
SPORTS ENTRY (Japanese)