Where can I buy old plastic Beyblades in Osaka (Japan)?

Hi! I'm Japanese.
You may find some plastic Beyblades in Mandarake.

There are 2 Mandarake stores in Osaka.
Mandarake Grand Chaos
Mandarake Umeda

I haven't been there so I'm not sure there are Beyblades. But Mandarake is good place so I think you'll enjoy if you go there.

If you are interested in Burst beyblades you may watch events.