You can try handling the KeyPress event and searching for the item
there.

private string match = "";
private int location = -1;

void listBox1_KeyPress(object sender, KeyPressEventArgs e)
{
   if (e.KeyChar == '\b')
   {
       location = -1;
       match = "";
       this.listBox1.SelectedIndex = 0;
   }
   else if (char.IsLetter(e.KeyChar))
   {
       match += e.KeyChar;
       int i = this.listBox1.FindStringExact(match);
       if (i > -1)
       {
           this.listBox1.SelectedIndex = i;
       }
       else if (location < this.listBox1.Items.Count - 1)
       {
           i = this.listBox1.FindString(match, location + 1);
           if (i > -1)
           {
               location = i;
               this.listBox1.SelectedItem = this.listBox1.Items[i];
           }
       }
       else
       {
           location = -1;
           match = "";
           this.listBox1.SelectedIndex = 0;
       }
   }
   e.Handled = true;
}

=====================
Clay Burch
Syncfusion, Inc.