I don't live in Osaka, so I don't know any places, but if you can read Japanese try this website
http://www.rokyu.net/pickup_prefecture28.html
It has a list of both indoor and outdoor courts. This one here,
http://www.rokyu.net/goal_detail554.html looks like its the closest to Moriguchi, although it looks like the court is sand, so it may not be the best place to ball. Here's another one that is kinda close.
http://www.rokyu.net/goal_detail555.html The comment says it's a pretty nice court but there a lot of kids and people who can't play there. It is close to a university though, so you might get some ballers out there.
The best thing to do would probably be to have look at that site then head out to a few courts and ask the people playing there whats up. I know most people I ball with play indoors for "circles" as well, so it might be a good idea to ask around and see if someone will invite you to join them.