I hope I can make friends when I visit Japan too, it can be hard if you can't spend a few weeks getting to know them I think.
I made a good friend a few months ago though. We met and just 'clicked' but she had to leave 3 days later!! We ended up staying penpals and now she has come to live in my city for a while with her boyfriend.
This has taught me that friendships can come from anywhere and if it's meant to be then you can make it work!
So have faith and I hope that you make some friends. ^_^