Generate combobox items from datagridview's distinct column values

On runtime I am changing some columns of datagridview into combobox columns. Now how do I get the existing distinct values in the combobox items? I am using entity model as datasource. My code is:

dgvLoadTable.DataSource = null;
                var context = new AdminEntities();
                var TableName = cboSelectTable.Text.ToString();
                var rawData = context.GetType().GetProperty(TableName).GetValue(context, null);
                var truncatedData = ((IQueryable<object>)rawData).Take(0);
                var source = new BindingSource { DataSource = truncatedData };
                dgvLoadTable.DataSource = source;
                dgvLoadTable.ReadOnly = false;
                dgvLoadTable.AllowUserToAddRows = true;


                for (int row= 0; row < dgvLoadTable.Rows.Count; row++)
                {
                 for (int col = 0; col < dgvLoadTable.Columns.Count; col++)
                       {
                           if (col == 2 || col == 4)
                           {
                               this.dgvLoadTable[col, row] = new DataGridViewComboBoxCell();

                              var item = dgvLoadTable.Rows.Cast<DataGridViewRow>().Where(r => r.Cells[0].Value != null).Select(r => r.Cells[col].Value).Distinct();
                               ((DataGridViewComboBoxCell)dgvLoadTable[col, row]).Items.AddRange(item.ToArray());
dgvLoadTable[col, row].ValueType = typeof(var);


                           }
                       }
                }


                dgvLoadTable.Refresh();

But this is not working, any suggestion?