Where are OS X sounds located in Finder?

I'm trying to make a short piece of music using only Mac and iPhone sounds using GarageBand. Cool, right?

However, I need the actual sound effects to make the song and I'm having trouble. I can't find many sounds on the internet and I thought you could find them in Finder. I've found all the error tones but that's it. No boot up sound, no trash sound, just the error tones. Is there another folder anywhere with all the tones?

And how would I get all the iPhone sound effects?