Code

foreach (Control c in calendar1.Controls)
{
	if (c.Visible && c is Button)
	{
		if ((c as Button).Image != null)
		{
			int width = c.Width;

			if (c.Left - width < 0)
			{
				// Its the right button
				Button b = new Button();
				b.Text = "<<";
				b.Size = c.Size;
				calendar1.Controls.Add(b);
				b.Location = new Point(c.Right, c.Top);
			}
			else
			{
				// Its the left button
				Button b = new Button();
				b.Text = ">>";
				b.Size = c.Size;
				b.Anchor = AnchorStyles.Right;
				calendar1.Controls.Add(b);
				b.Location = new Point(c.Left - width, c.Top);
			}
		}
	}
}