Getting a Visual Studio built-in commandbar to add buttons to it is not so easy as it may seem. You have the DTE.CommandBars collection, but:

– To retrieve a commandbar by name, you have to guess its name first. See: HOWTO: Guessing the name of a command bar to add a custom menu entry in Visual Studio .NET add-ins

– If the commandbar is not a “root” commandbar, but a commandbar popup, it may not be indexed in that collection, so it is better to get it from the parent CommandBar.Controls collection, but it is not so easy. See: HOWTO: Locate commandbars in international versions of Visual Studio

– Some command bar names are dupplicated.

There is other way to get a commandbar, using its Guid and Id that are truly unique. But this has also some tricks as explained in my latest article:

HOWTO: Get a CommandBar by Guid and Id rather than by name from a Visual Studio add-in
http://www.mztools.com/articles/2011/MZ2011004.aspx