gistfile1.txt

var types = AppDomain.CurrentDomain.GetAssemblies()
    .SelectMany(assem => assem.GetTypes()
        .Select(t => t)
        .Where(t => t.FullName.Contains("Namespace.Foo"))
        .Where(t => Attribute.GetCustomAttributes(t, typeof(BarAttribute)).Length > 0)
        .Select(t => t)
    );

foreach(Type typ in types)
{
    var instance = Activator.CreateInstance(typ);
}