Under normal circumstances you should get the Scandit Barcode Scanner directly through NuGet.org. This will allow you to very easily add the barcode scanning functionality to your project. For details, take a look at the integration guides for iOS, and Android.

To add a NuGet package you already have installed on your system, you will need to configure a local package source. For Xamarin Studio, you can follow these instructions. For Visual Studio, check the package sources section.