Hi PandaChey
Most of the brushes came in the fan made translation pack before there was a developer supported English version.
It's available here:
[link]It uses the same license file as purchased from the developer so I'm pretty sure you can just re-install over the top to use this "enhanced" version of the program instead.
I also tend to make my own brushes for certain tasks, these are just tweaked and saved versions of the standard ones.
There's a very handy tutorial here on dA for SAI:
[link]If you're looking for the actual files, it doesn't install like a standard program so they're hard to find. On my W7 machine they are here;
"C:\Users\User\AppData\Local\Zame\PaintTool SAI English Pack"
Brushes are actually just text .ini files if you want to go digging through them to see how they're configured, but it's not necessary!
I hope that helps? Feel free to ask if anything isn't clear.