public partial class MainWindow : INotifyPropertyChanged
{
  public MainWindow()
  {
    InitializeComponent();
    Numbers = Enumerable.Range(0, 10).Select(n => new NumbersSource(n)).OrderBy(ns => ns.From).ToList();
    DataContext = this;
  }

  public List<NumbersSource> Numbers { get; private set; }

  NumbersSource _selectedItem;
  public NumbersSource SelectedItem
  {
    get { return _selectedItem; }
    set
    {
      _selectedItem = value;
      PropertyChanged(this, new PropertyChangedEventArgs("SelectedItem"));
    }
  }

  public event PropertyChangedEventHandler PropertyChanged;
}

public class NumbersSource
{
  public NumbersSource(int from)
  {
    From = from;
    Numbers = Enumerable.Range(from, 10 - from).ToList();
  }

  public int From { get; private set; }
  public List<int> Numbers { get; private set; }
}

<Grid>
  <Grid.RowDefinitions>
    <RowDefinition />
    <RowDefinition />
  </Grid.RowDefinitions>
  <ComboBox
    x:Name="MasterSource"
    VerticalAlignment="Center"
    ItemsSource="{Binding Numbers}"
    DisplayMemberPath="From" />
  <ComboBox
    Grid.Row="1"
    VerticalAlignment="Center"
    ItemsSource="{Binding SelectedItem.Numbers, ElementName=MasterSource}" />
</Grid>

<Grid>
  <Grid.RowDefinitions>
    <RowDefinition />
    <RowDefinition />
  </Grid.RowDefinitions>
  <ComboBox
    VerticalAlignment="Center"
    ItemsSource="{Binding Numbers}"
    SelectedItem="{Binding SelectedItem, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"
    DisplayMemberPath="From" />
  <ComboBox
    Grid.Row="1"
    VerticalAlignment="Center"
    ItemsSource="{Binding SelectedItem.Numbers}" />
</Grid>