This is a project called eTandem that was funded by the EU in 2001.
It is a matching service for language learners who want to practice with a native speaker.
http://www.tcd.ie/CLCS/tandem/etandem/etindex-en.html
You submit a form to eTandom and they try to match you to someone of similar skill. It's for all languages not just Japanese, and while I notice most Japanese seem to want English there are possibilities to exchange a language other than English.
At the time of writing this there are 32 Japanese awaiting placement with a partner.
http://slf4.slf.ruhr-uni-bochum.de/pa/p ... input=Show
(mostly English but if you have Korean, Chinese or German as a native language your luck might be in)
Even if you don't want to search for a partner using eTandem They have good sections on Tandem learning tips and activities
http://www.slf.rub.de/etandem/ethilfen-en.html
http://www.slf.rub.de/email/help/helpen ... #questions
http://www.slf.rub.de/tandem/inh01-eng.html
It's not as easy as it seems to do language exchange and help someone else learn. But if you manage to find a partner you can work with it can be very satisfying.
