Visual Basic (.NET) > randomize listbox picks (unique) - vb.net

Question

I just want to make randomizer program. It will be used to pick tournament pairs (like f.e. UEFA Champions League quaterfinal pairs)
GUI Screen: http://i.imgur.com/jqBMJjt.png
I have trouble with this.. When I tried to make picker, it works well > from listbox 1 (left side) to listbox2 (50% of listbox1 items), listbox3 (50% of listbox1 items).. (left side) but these picks aren't unique. There are some duplicates as you can see on image (2nd listbox 2x noob).
Part of my code:
Private Sub RandomiseListBox()
Dim count As Integer = CarbonFiberListBox1.Items.Count
Dim countt As Integer
'countt = count / 2
Dim item As String
Dim itemz As New List(Of String)()
Dim repeat As New List(Of String)()
Dim aa, bb As Integer
If Not count = 0 And ((count Mod 2) = 0) Then
CarbonFiberListBox2.Items.Clear()
CarbonFiberListBox3.Items.Clear()
For index As Integer = 0 To countt - 1 Step 1
item = Me.CarbonFiberListBox1.Items(Me.randomiser.Next(index, count))
itemz.Add(item)
'Me.CarbonFiberListBox1.Items.Remove(item)
'Me.CarbonFiberListBox1.Items.Insert(index, item)
Me.CarbonFiberListBox2.Items.Insert(index, item)
Next index
For index As Integer = 0 To countt - 1 Step 1
For aa = 0 To bb = 999
item = Me.CarbonFiberListBox1.Items(Me.randomiser.Next(index, count))
If Not (itemz.Contains(item)) And Not (repeat.Contains(item)) Then
repeat.Add(item)
'Me.CarbonFiberListBox1.Items.Remove(item)
'Me.CarbonFiberListBox1.Items.Insert(index, item)
Me.CarbonFiberListBox3.Items.Insert(index, item)
End If
Next
Next index
'For index As Integer = 0 To countt - 1 Step 1
'Next index
ElseIf count > 0 Then
'CarbonFiberButton4.Text = "ODD PARTICIPANTS!"
Else
End If
End Sub
Can I get help? I think it is so easy.

Answer 1

Maybe this little example will give you an idea. It works by getting a list, in random order, from one listbox. Note how the list is depleted as items are added to the other listboxes which stops duplicates.
Private Sub Button2_Click(sender As Object, e As EventArgs) Handles Button2.Click
'some sample data
ListBox1.DataSource = {"one", "two", "three", "four", "five", "six", "seven"}
DoRandom()
End Sub
Private Shared prng As New Random
Private Sub DoRandom()
ListBox2.Items.Clear()
ListBox3.Items.Clear()
Dim l As New List(Of String)
'random order of items in ListBox1
l.AddRange(ListBox1.Items.Cast(Of String).OrderBy(Function(s) prng.Next))
'add half to lb2
For x As Integer = 0 To l.Count \ 2
ListBox2.Items.Add(l(0))
l.RemoveAt(0)
Next
'remainder to lb3
For x As Integer = 0 To l.Count - 1
ListBox3.Items.Add(l(0))
l.RemoveAt(0)
Next
End Sub