Referencing system.management.automation.dll in Visual Studio
System.Management.Automation on Nuget
System.Management.Automation.dll on NuGet, newer package from 2015, not unlisted as the previous one!
Microsoft PowerShell team packages un NuGet
Update: package is now owned by PowerShell Team. Huzzah!
A copy of System.Management.Automation.dll is installed when you install the windows SDK (a suitable, recent version of it, anyway). It should be in C:\Program Files\Reference Assemblies\Microsoft\WindowsPowerShell\v1.0\
If you don't want to install the Windows SDK you can get the dll by running the following command in powershell:
Copy ([PSObject].Assembly.Location) C:\