There are actually quite a few J-punk bands, but some of them are older bands like The Stalin, Balzac, and Coaltar of the Deepers so most people don't know about them.
I uploaded a few songs from some of the bands
The Stalin - Stop girl mp3
http://www.sendspace.com/file/dmj5ho
The Mad Capsule Markets - XXX Can of this mp3
http://www.sendspace.com/file/fbpmi7
Coaltar of the Deepers - Dead by Dawn mp3
http://www.sendspace.com/file/ekm3pb
Balzac - Wall mp3
http://www.sendspace.com/file/os9ob5
Charcoal Filter - Brand New Myself~Boku ni dekiru koto
http://www.sendspace.com/file/ytvqdy
Last Alliance - Rebel Fire mp3
http://www.sendspace.com/file/fm6mlp