How to random order a 3 digit number on a list box?

Question

How to random order a 3 digit number on a list box?
For example, When I add any 3 digit number on a list box to this number 647 = $23 The result is:

647 = $23  
674 = $23
476 = $23 
467 = $23
746 = $23
764 = $23

How to code the above result?
My previous code right now.

public partial class frmJaialai : Form
{
    List<Jaialai> source;

    public frmJaialai()
    {
        InitializeComponent();
    }

    private void frmJaialai_Load(object sender, EventArgs e)
    {
        source = new List<Jaialai>();

        FillJaialaiListBox();
    }

    private void btnAdd_Click(object sender, EventArgs e)
    {
        if (IsValidData())
        {
            int bet;
            if (string.IsNullOrEmpty(txtJaialaiNumber.Text) || !Int32.TryParse(txtBet.Text, out bet))
            {
                MessageBox.Show("Must be a required field.", "Entry Error");
                return;
            }
            var existingProduct = source.Where(x => x.JaialaiNumber == Convert.ToInt32(txtJaialaiNumber.Text)).SingleOrDefault();
            if (existingProduct != null)
            {
                existingProduct.Bet += bet;
            }
            else
                source.Add(new Jaialai { Bet = bet, JaialaiNumber = Convert.ToInt32(txtJaialaiNumber.Text) });

            FillJaialaiListBox();
            SaveJaialais();

            txtJaialaiNumber.Text = "";
        }                          
    }             
    private void btnRumble_Click(object sender, EventArgs e)
    {

    }
    public class Jaialai
    {
        public int JaialaiNumber { get; set; }
        public int Bet { get; set; }

        public override string ToString()
        {
            return string.Format("{0} = {1}",
                JaialaiNumber.ToString(), Bet.ToString("c"));
        }
    }

    private void SaveJaialais()
    {
        // save the jai-alai numbers list on a txt file
        const string dir = @"C:\Automated Jai-alai Program\";
        const string path = dir + "Jai-alai Numbers List.txt";

        System.IO.StreamWriter SaveFile = new System.IO.StreamWriter(path);
        foreach (var item in lstJaialaiNumbersList.Items)
        {
            SaveFile.WriteLine(item);
        }

        SaveFile.Close();
    }     

    private void FillJaialaiListBox()
    {
        lstJaialaiNumbersList.Items.Clear();
        foreach (Jaialai j in source)
        {
            lstJaialaiNumbersList.Items.Add(j.ToString());
        }
    }