WPF

public static T FindChild<T>(DependencyObject child) where T : FrameworkElement
{
  if (child.GetType() is typeof(T)) return child;

  for (int count = 0; count < VisualTreeHelper.GetChildrenCount(child); count++)
  {
    var childItem = VisualTreeHelper.GetChild(child, count);
    var result = FindChild(childItem);
    if (result == null) continue;
    return result;
  }
  return null;
}

private ScrollViewer _instanceViewer;

private void ScrollUp()
{
  if (_instanceViewer == null)
    _instanceViewer = FindChild<ScrollViewer>(myListViewInstance);
  if _instanceViewer == null) return;
  _instanceViewer.LineUp();
}

private void ScrollDown()
{
  if (_instanceViewer == null)
    _instanceViewer = FindChild<ScrollViewer>(myListViewInstance);
  if _instanceViewer == null) return;
  _instanceViewer.LineDown();
}