I used System.Windows.Controls.Calendar as follows:

(which is in Hebrew, but I would have guessed that you have an idea ...)
XAML:
<Calendar Name="dteSelectedMonth" DisplayMode="Year" SelectionMode="None"
DisplayModeChanged="dteSelectedMonth_DisplayModeChanged" />
Year:
private void dteSelectedMonth_DisplayModeChanged(object sender, CalendarModeChangedEventArgs e)
{
dteSelectedMonth.DisplayMode = CalendarMode.Year;
}
dteSelectedMonth.DisplayDate, .
, Expander ComboBox SelectedMonth