In my case ServiceConfigurationFactory class helped me. Below is peace of code how I'm retrieving IOrganizationService instance:
ClientCredentials credentials = new ClientCredentials();
credentials.UserName.UserName = "username";
credentials.UserName.Password = "password";
IServiceConfiguration<IOrganizationService> config = ServiceConfigurationFactory.CreateConfiguration<IOrganizationService>(organizationUriIFD);
using (Microsoft.Xrm.Sdk.Client.OrganizationServiceProxy _serviceProxy = new OrganizationServiceProxy(config, credentials))
{
// This statement is required to enable early-bound type support.
_serviceProxy.ServiceConfiguration.CurrentServiceEndpoint.Behaviors.Add(new ProxyTypesBehavior());
IOrganizationService _service = (IOrganizationService)_serviceProxy;
WhoAmIResponse response = (WhoAmIResponse)_service.Execute(new WhoAmIRequest());
Console.WriteLine(response.UserId.ToString());
Console.ReadLine();
}