open your stock firmware .zip file in 7zip and extract it from in there.
EDIT:
Anticipating your next question, they are in:
system\framework\framework-res.apk\res\drawable-hdpi
look at stat* icons, and in particular stat_sys_data* icons.
You would have to use an existing theme zip, and replace the particular icons you want to change. Its not just as simple as copying icons over to somewhere on the device I'm afraid. They are built into the .apk files themselves.