Location of Ribbon XML & Action JS for Ribbon

Location of Ribbon XML file is :

C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\14\TEMPLATE\GLOBAL\XML\CMDUI.XML

Action JS code for most of these ribbon elements you can find here:

C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\14\TEMPLATE\LAYOUTS\SP.Ribbon.debug.js

Actions for rich text editor ribbon are stored here:

C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\14\TEMPLATE\LAYOUTS\SP.UI.Rte.debug.js