using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApplication30
{
    class Program
    {
        static void Main(string[] args)
        {
            var e1t = Create<E1>();
            var e2t = Create<E2>();
            var e3t = Create<E3>();
        }

        public static MyBaseGeneric<T> Create<T>()
            where T : E
        {
            foreach (var a in AppDomain.CurrentDomain.GetAssemblies())
            {
                var type = a.GetTypes().FirstOrDefault(t => t.BaseType == typeof(MyBaseGeneric<T>));

                if (type != null)
                    return (MyBaseGeneric<T>)Activator.CreateInstance(type);
            }

            throw new InvalidOperationException();
        }
    }

    public class E {}

    public class E1 : E { }
    public class E2 : E { }
    public class E3 : E { }

    public class MyBaseGeneric<T> where T : E { }

    public class MyDerivedE1 : MyBaseGeneric<E1> { }
    public class MyDerivedE2 : MyBaseGeneric<E2> { }
    public class MyDerivedE3 : MyBaseGeneric<E3> { }

}