How do I get the RS232 ports that are being used?

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.IO.Ports;
using System.Windows.Forms;
using System.Management;

namespace Detect_USB2
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
            SerialPort ComPort = new SerialPort();

            chkSP();
        }
        private void chkSP()
        {
            ManagementObjectSearcher searchType = new ManagementObjectSearcher("SELECT * FROM Win32_SerialPort");

            foreach (ManagementObject moDiskete in searchType.Get())
            {
                if (!listBox1.Items.Contains(moDiskete["Name"]))
                {
                    
                    listBox1.Items.Add(moDiskete["Name"].ToString());

                }
            }            
        }
        private void MyTimer_Tick(object sender, EventArgs e)
        {
         listBox1.Items.Clear();
            chkSP(); 
        }
        private void Form1_Load(object sender, EventArgs e)
        {
            Timer MyTimer = new Timer();
            MyTimer.Interval = (5 * 1000); // 1 mins
            MyTimer.Tick += new EventHandler(MyTimer_Tick);
            
            MyTimer.Start();
        }  
    }
}