The only reference I have is from a Killer7 fan website, and I believe it's overtracked
Killer 7 software sales (PS2 and GC combined) :
Japan: 12,000 copies
North America: 150,000 copies
Europe: 100,000 copies
Meaning around 370 k on it's lifetime.
No More Heroes is already beyond that and it's only out for a few weeks.
Vgcharts has the following number for PS2 version in Japan
Launch sales
1) 1,575
2) 394
3) 165
(...)