Getting an internship is a matter of finding a company you want to work for and convincing them you'll provide enough value to them.
Pycon.jp would be a good place to meet developers and find companies, but it looks like it is already sold out. You could still take a look at their sponsor list to see if you can find any interesting companies.
You could also get involved in the local international developer events, like Tokyo Rubyist Meetup, Hacker News Tokyo, and Tokyo iOS Meetup.
To demonstrate value to companies, you can work on building up your personal profile. When reaching out to any companies, demonstrate why you want to work for that company (as opposed to other ones), and show how you can provide value. Hired Fast is a book aimed at Junior developers, but I think it gives a great overview of the mindset needed to get a job (or internship).