Bind properties from a ViewModel to another model

I'm curious about binding properties from a ViewModel to another Model.

ViewModel:

public class StoreIndexData
    {
    public Store Stores { get; set; }
    public District Districts { get; set; }
    public Department Departments { get; set; }
    }

Important note: I use a ViewModel because I need these models together in order to make a cascading dropdownlist to work, however this model is not added in the DB context.

In the view, the user can pickup a Department, then the dropdownlist forDistrict populates, and finally the user adds the information of the Store.

Problem: The problem comes when I want to save the properties the user wrote inside the Store model, since the view is constructed using:

@model Application.Models.ApplicationviewModels.StoreIndexData

and the inputs point to this model.

Relevant info:

This is my view. I access each model from the ViewModel (Department, District, Stores) in order to get each property:

<form asp-action="Create" role="form"><div asp-validation-summary="ModelOnly" class="text-danger"></div><div class="modal-body form-horizontal"><div class="form-group"><label asp-for="Departments.DepartmentID" class="col-md-2 control-label"></label><div class="col-md-10"><select asp-for="Departments.DepartmentID" class="form-control"
                        asp-items="@(new SelectList(@ViewBag.ListofDepartment,"DepartmentID","DepartmentName"))"></select></div></div><div class="form-group"><label class="col-md-2 control-label">District</label><div class="col-md-10"><select class="form-control" id="DistrictID" name="DistrictID" asp-for="Departments.DistrictID"
                        asp-items="@(new SelectList(string.Empty,"DistrictID","DistrictName"))"></select></div></div><div class="form-group"><label asp-for="Stores.StoreChainID" class="col-md-2 control-label"></label><div class="col-md-10"><select asp-for="Stores.StoreChainID" class="form-control" asp-items="ViewBag.ChainList"></select><span asp-validation-for="Stores.StoreChainID" class="text-danger"></span></div></div><div class="form-group"><label asp-for="Stores.StoreName" class="col-md-2 control-label"></label><div class="col-md-10"><input asp-for="Stores.StoreName" class="form-control" /><span asp-validation-for="Stores.StoreName" class="text-danger"></span></div></div><div class="form-group"><label asp-for="Stores.StoreAddress" class="col-md-2 control-label"></label><div class="col-md-10"><input asp-for="Stores.StoreAddress" class="form-control" /><span asp-validation-for="Stores.StoreAddress" class="text-danger"></span></div></div><div class="form-group"><label asp-for="Stores.StoreArea" class="col-md-2 control-label"></label><div class="col-md-10"><input asp-for="Stores.StoreArea" class="form-control" /><span asp-validation-for="Stores.StoreArea" class="text-danger"></span></div></div>
        @await Html.PartialAsync("_ModalFooter", new ModalFooter { })</div></form>

The trick must come here I suposse, in the Post method:

[HttpPost, ActionName("Create")]
        [ValidateAntiForgeryToken]
        public async Task<IActionResult> Create(int? id, [Bind("StoreID,DistrictID,StoreChainID,StoreName,StoreAddress,StoreArea")]Store store)
        {
            if (ModelState.IsValid)
            {
				bool isNew = !id.HasValue;
				if (isNew)
				{
					_context.Add(store);
					await _context.SaveChangesAsync();
					return RedirectToAction("Index");
				}
				var storetoupdate = await _context.Stores.SingleOrDefaultAsync(s => s.StoreID == id);
            }
            ViewData["DistrictID"] = new SelectList(_context.Districts, "DistrictID", "DistrictID", store.DistrictID);
            ViewData["StoreChainID"] = new SelectList(_context.StoreChains, "StoreChainID", "StoreChainID", store.StoreChainID);
            return RedirectToAction("Index");
        }

First, I would need to change:

[Bind("StoreID,DistrictID,StoreChainID,StoreName,StoreAddress,StoreArea")]Store store)

For the ViewModel StoreIndexData.

But then, I'm lost. Maybe if I put a conditional when 

            if (!ModelState.IsValid)

And since this will be true, initialize a new Store model with the values that are coming from the Post method, but I don't know how to do this.

Thanks in advance for any help, I hope the problem is clear.

Regards,