Hey man,
there is a tournament in September and it lasts 15 days, so unless you want to see the final day, I am sure you can get tickets relatively easily. Remember, these are events that start in the morning and go on for several hours, so I wouldn't go there right at the beginning or else you'll get pretty bored by the team the big fights (usually later in the day) start.
The tickets? See here:
http://www.sumo.or.jp/eng/ticket/kaikata/index.html
Best to get a buddy of your brother who speaks Japanese to call one of the vendors listed on the link above and make the purchase.
Enjoy
