Here's how you can find a language partner on Italki:

[These instructions work for the English version of the website]

1. Go to "Community" (to the right of "Find a teacher" on the computer version)

2. Select "Language Partners"

3. Choose the language you wish to learn. I suppose for you it would be either English or Japanese.

4. Check the box "native speaker"

5. You will also see the "Learning" menu. Select "Chinese". It will allow you to meet people who are learning Chinese, which will make the language exchange much easier.

6. Click on "browse".

7. See everyone who speak English natively and who are learning Chinese. Select one (or many) learners, send them a message, introduce yourself and tell them why you wish to speak with them. I always prefer to send messages to those who have written something on their profile, it allows me to say something interesting or to be curious about them. If you just say "hi, how are you", people might ignore you. 

8. Enjoy meeting someone new, exchanging languages and potentially making a new friend :)

***BEWARE*** There are many perverts or people looking for girlfriends. Make sure that those talking with you are serious learners. If they ask for pictures, they compliment you on your look or they want to add you on Skype (or any other messaging app) and you barely talked with each other, that's a bad sign.