The DevComponents.DotNetBar2.dll is a commercially available product and not free:
http://www.devcomponents.com/dotnetbar/[
^]
Therefor you won't be able to get the source code for this without paying for it.
For designing your application I can always recommend the DeveloperExpress tools. These allow you to create a skin which styles your application. The skin can be created with their skineditor tool, and even a designer can do this without any programming knowledge.