How long will you be in Osaka?
Which part of the city will you be in?
When you say you want to see Japanese cycling... do you mean retail, on the street, racing...?
You might have a chance to see some keirin while you're here... at least on TV if you can't get around...
There's a 'bicycle museum' in Sakai (home of Shimano), in southern Osaka Prefecture.
Here are links:
http://www.kansai.meti.go.jp/english.../kohyo/128.htm
This is the museum's official site... all in Japanese, but with lots of graphics:
http://www.h4.dion.ne.jp/~bikemuse/index0.html
eta:
The prices for imported bikes aren't much higher than you'd pay retail in the States, considering currency exchange rates. You may find something unique or otherwise unavailable in the States in bike shops here, but there's a big demand for American and European bike products, so, you'll see a lot of familiar stuff.