Filesystem:/System/Library/SpringBoardPlugins/Assistant.uibundle

Summary
According to iOS 5.x, Siri UI files and Mic Artwork are located at: /System/Library/CoreServices/SpringBoard.app Then in iOS 6, these files have been moved to here.

In iOS 7, all images have either been moved to somewhere else or do not exist.

Parents
Root/System/Library/SpringBoardPlugins