Participate in meetup.com events? There are many international cultural exchange meetup groups and holds party sometimes. People who want to speak English (or other languages) and meet people from abroad go to such parties.
Using Hub Japan's BE A LOCAL lets you meet local Japanese, too :)
I think the fastest and most effective way to find them is online. But if you want to find them face to face, then go to a bar that is popular among foreigners is the most effective I think.