Instantiate repository classes dynamically

I'm curious about the best way to instantiate my repositories. Currently they're in the main controllers constructor method.

I was thinking making separate controllers for inbounds, outbounds, directs then instantiate the correct repository in the controller constructor. But that seems redundant in some ways.

I am wondering if I should have some sort of factory method that will load the proper repository when it's called from the controller. What do you folks think?

Note: I understand that implementing these design patterns are not required to be used for an application this simple but I want to learn it for educational purposes.

Generic repository interface:

namespace DirectOrderTracker.Services
{
    interface IRepository<T1> where T1 : class
    {
        IEnumerable<T1> GetAllSales(string commodity);
        void EditSale(T1 obj);
        void SaveChanges();
    }
}

Main controller:

namespace DirectOrderTracker.Controllers
{
    public partial class GridController : Controller
    {
        private SalesService salesService;
        private DirectRepository directs;
        private InboundRepository inbounds;
        private OutboundRepository outbounds;
        public GridController()
        {
            salesService = new SalesService(new OrdersEntities());

< start >Here is where I want to improve my code:

            directs = new DirectRepository(new OrdersEntities());
            inbounds = new InboundRepository(new OrdersEntities());
            outbounds = new OutboundRepository(new OrdersEntities());

< end >

        }
        /*
         * 
         *OUT-BOUND SALES
         * 
         */
        public ActionResult AllOutBounds([DataSourceRequest] DataSourceRequest request, DateTime? fromDate, DateTime? toDate, string commodity)
        {
            var result = outbounds.GetAllSales(commodity);

            return Json(result.ToDataSourceResult(request), JsonRequestBehavior.AllowGet);
        }
        [AcceptVerbs(HttpVerbs.Post)]
        public ActionResult EditOutBounds([DataSourceRequest] DataSourceRequest request, OutboundSalesViewModel sale)
        {
            if (sale != null && ModelState.IsValid)
            {
                outbounds.EditSale(sale);
                outbounds.SaveChanges();
            }
            return Json(new[] { sale }.ToDataSourceResult(request, ModelState));
        }
        /*
         * 
         *IN-BOUND SALES
         * 
         */
        public ActionResult AllInBounds([DataSourceRequest] DataSourceRequest request, DateTime? fromDate, DateTime? toDate, string commodity)
        {
            var result = inbounds.GetAllSales(commodity);

            return Json(result.ToDataSourceResult(request), JsonRequestBehavior.AllowGet);
        }
        [AcceptVerbs(HttpVerbs.Post)]
        public ActionResult EditInBounds([DataSourceRequest] DataSourceRequest request, InboundSalesViewModel sale)
        {
            if (sale != null && ModelState.IsValid)
            {
                inbounds.EditSale(sale);
                inbounds.SaveChanges();
            }
            return Json(new[] { sale }.ToDataSourceResult(request, ModelState));
        }
        /*
         * 
         *DIRECT SALES
         * 
         */
        public ActionResult AllDirects([DataSourceRequest] DataSourceRequest request, DateTime? fromDate, DateTime? toDate, string commodity)
        {
            var result = directs.GetAllSales(commodity);

            return Json(result.ToDataSourceResult(request), JsonRequestBehavior.AllowGet);
        }

        [AcceptVerbs(HttpVerbs.Post)]
        public ActionResult EditDirects([DataSourceRequest] DataSourceRequest request, DirectSalesViewModel sale)
        {
            if (sale != null && ModelState.IsValid)
            {
                directs.EditSale(sale);
                directs.SaveChanges();

                sale.Margin = Calculations.MarginCalc(sale.Qty, sale.UNITPRICE, sale.UNITCOST, sale.POFrghtRate);
            }
            return Json(new[] { sale }.ToDataSourceResult(request, ModelState));
        }

        public ActionResult GetSalesPeople()
        {
            return Json(salesService.GetAllSalesPeople(), JsonRequestBehavior.AllowGet);
        }

        public ActionResult GetAllCommodities()
        {
            return Json(salesService.GetAllCommodities(), JsonRequestBehavior.AllowGet);
        }
    }
}

Sample Inbound Repository:

public class InboundRepository : IRepository<InboundSalesViewModel>
    {
        private OrdersEntities entities;
        public InboundRepository(OrdersEntities entities)
        {
            this.entities = entities;
        }
        public IEnumerable<InboundSalesViewModel> GetAllSales(string commodity)
        {
            return entities.CustPOLines
                           .Where(x => x.WAREHOUSE != "~D")
                           .OrderByDescending(x => x.ModifyDate)
                            .Select(s => new InboundSalesViewModel
                            {
                                CustPOLineID = s.CustPOLineID,
                                VendDesc = s.Vendor.VendDesc,
                                FreshouseRefNum = s.FreshouseRefNum,
                                Qty = s.Qty.HasValue ? s.Qty.Value : default(decimal),
                                Cost = s.Cost.HasValue ? s.Cost.Value : default(decimal),
                                CostAlt = default(decimal),
                                PPROREFDATE = s.PPROREFDATE,
                                CarrierDesc = s.CarrierDesc,
                                LineFrghtRate = s.LineFrghtRate.HasValue ? s.Cost.Value : default(decimal),
                                VendPurchPONum = s.VendPurchPONum,
                                POLineComment = s.POLineComment,
                                Commodity = s.Product.Commodity,
                                LoadNumber = s.LoadNumber,
                                ProdDesc = s.Product.ProdDesc,
                                TYPE = s.TYPE,
                                Buyer = s.Buyer
                            })
                        .ToList();
        }

        public void EditSale(InboundSalesViewModel sale) {
            var existingSale = entities.CustPOLines.Find(sale.CustPOLineID);
            existingSale.POLineComment = sale.POLineComment;
            entities.Entry(existingSale).State = EntityState.Modified;
        }

        public void SaveChanges()
        {
            entities.SaveChanges();
        }

    }

Perhaps Dependency Injection is what I'm looking for? http://blog.agilistic.nl/a-step-by-step-guide-to-using-ninject-for-dependancy-injection-in-c-sharp/