[Firebird]

Its quite common to see people play guitar on the street in every major city. But i´ve never seen any of them collect money, so you would have a hard time.
Japanese (mostly young) people play on the street just to show what they can do or to promote their band or sell their cds. Usually Friday and Saturday nights are busy in or around trainstations and huge public spaces as well as covered shopping arcades. I´ve seen police send them away once, but usually its tolerated.
But as i said, none of them is collecting money. I could imagine you might be able to sell your own cds if you are good but thats it. Also speaking a bit of japanese might be handy.