I see some classess I would Like to use here https://github.com/mono/monodevelop/tree/master/main/src/addins/MacPlatform/MacInterop
But I cannot find the dll where the namespace MonoDevelop.Macinterop resides in??
it's in MacPlatform.dll
Since that dll depends on several other large MonoDevelop dlls, I would recommend you copy the code you need into your own project.