There aren't any cons that I know of, but at the end of March this year there was the Anime Contents Expo. Although, it doesn't look like it has been decided if there will be another one next year as I can't find any details about it.
English website - http://www.animecontentsexpo.jp/english.html
, but the Japanese site has much more information on it.
Failing that, you could go to a Japanese cosplay event, meet some other cosplayers and get some awesome photos!
FYI, there are very few cons throughout the year that you can cosplay at in Japan. The more common thing is to go to a cosplay event, which is a completely separate thing and not like how we do it outside Japan at all.