StructuremapFactory.cs

public class Scratchpad
{
    [Fact]
    public void When_testing_something()
    {

        var container = new Container(c =>
        {
            c.Scan(a =>
            {
                a.TheCallingAssembly();
                a.WithDefaultConventions();
                a.AddAllTypesOf<ISource>();
            });

            c.For<ISource>().Use(context => context.GetInstance<SourceFactory>().GetSource("first"));
        });

        container.GetInstance<ISource>().ShouldBeOfType<FirstSource>();

    }
}

public class SourceFactory
{
    private readonly List<ISource> _sources;

    public SourceFactory(IEnumerable<ISource> sources)
    {
        _sources = sources.ToList();
    }

    public ISource GetSource(string name)
    {
        return _sources.Single(s => s.Name.Equals(name, StringComparison.OrdinalIgnoreCase));
    }
}

public interface ISource
{
    string Name { get; }
}

public class FirstSource : ISource
{
    public string Name { get { return "First Source"; } }
}

public class Second : ISource
{
    public string Name { get { return "Second Source"; } }
}