If it’s January, May, or September, you can head over to a Lawsons to try and use the Japanese-language machines to get tickets to a sumo match in Ryogoku. It’d probably be better to have a Japanese friend or the concierge help you out. Even better, you can try to get to a sumo-heya training camp in Ryogoku. This article explains how to do it, and this list tells you which heya training camps may be open to visitors.