I think they come with ITG2PC, except some ITG1 songs are missing. You can get them through a link provided on this page, although it's not working at the moment.
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QWERTYkid911: If someone posts porn, then this thread will perfectly represent the internet.
Slowpoke: Ah, so that's how He created the universe so quickly... He was hopped up on caffeine. Thanks for clearing up that philosophical mystery...
PooingCavy: (About difficulty levels) If I could make it up, it would be: Water, Soda, Coffee, Red Bull, ADHD