If you download the source code from the codeplex link you mentioned, it also includes the source for WPF. This is version 3.5, but it should not be a huge deal.
If you want only DataStateSwitchBehavior, you can start a new project, add the source files:
BindingListener.cs ConverterHelper.cs DataStateSwitchBehavior.cs GoToState.cs
and add a link to the dll Blend. It compiles and works.
Joshvarga
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