The sounds come from a bunch of places. There are some stock things that just come with RPGMaker: the ZAP of the earclips is one of those. Then there's stuff I individually hunt down from various sites, sometimes tweaking a bit. And then, for GT, there's a project some people put together a few years ago called the OpenNSFW pack that has a ton of really useful odds and ends. I don't think any of that was used in CS 1 though.
Lest anyone ascribe too much meaning to "unused" sounds though, aside from the stock RPGMaker stuff, it's really just a case of me having a few different possibilities, tossing them into the folder to experiment with, and then using or not using depending on how well they work. Sometimes you think something will fit and it just doesn't for whatever reason. And then I never get around to deleting the unused stuff.