If you are planning on living, or are already living in Japan, the bigger cities are probably your best bet for finding a girl for whatever reason, be it dating, friendship, hook-ups, etc. Girls in the cities on average have better English and can meet you halfway with your Japanese. My time spent in more rural areas yielded fruitless results.
If clubs are your thing, then foreigners can have a bit easier time finding a partner strictly from the fact that they are foreign. Some girls go to clubs looking for foreign guys, and in many cases, Japanese skill can be icing on the cake (although some only want to hear English). One girl I was talking to found out I spoke a bit of Japanese, and she turned to her friend and said "Ikeru" or "I can go for that". A friend of mine who doesn't speak a lick of Japanese just goes up to girls, tries English, and surprisingly often gets decent results, despite it being hit and miss.
This isn't always the case of course, but foreigners typically have it easier in clubs, with Japanese skill opening more doors.
If clubs are not your thing, many cities have different groups of international get-togethers, where Japanese people who sign up to go to the barbeques, theme park outings, bar meet-ups, etc., are interested in meeting foreigners, and will often keep the conversation going once you start talking (if that is something you are worried about).
Of course, girls are girls no matter where you go. If you look half decent, don't dress like a slob, and are nice to talk to, you should be good to go.
Even though it's a late response, I hope this helps. It's only my experience from living in Japan (still here!).
