Create Method
public static IEnumerable<Control> GetControlsOfType<T>(Control control)
{
var controls = control.Controls.Cast<Control>();
return controls.SelectMany(ctrl => GetControlsOfType<T>(ctrl)).Concat(controls).Where(c => c is T);
}
And use it Like
Var controls= GetControlsOfType<TextBox>(this);//You can replace this with your control