For Num As Integer = IndexCounter To (FixedValues.Count - 1I) Step NumStep

        FixedValues =
            (Result1.Concat(Result2).Concat(Result3)).
            Distinct.
            Select(Function(Value As Integer)
                       Return If(Value < MAX, Value, Rand.Next(0, MAX))
                   End Function).ToArray

        Dim Rand As New Random

    Private Sub Test() Handles MyBase.Shown

Imports System.IO
Public Class Form1
 
    Dim maximum As Short = 99
    Dim x As Integer = 0
    Dim Número As Double
    Private TextBoxes As TextBox() = {Nothing}
    Private Result1 As Int32(), Result2 As Int32(), Result3 As Int32()
    Private _textBox As Object
    Private Property ListBox1Count As Integer
    ReadOnly MAX As Integer = 99
    ReadOnly Randomizer As New Random
    Dim Combo As List(Of Integer) = Nothing
    Dim Combos As New List(Of List(Of Integer))
 
    Dim FixedValues As Integer() = Nothing
    ReadOnly RandomValues As Integer() =
        Enumerable.Range(0, 99).ToArray
 
 
    Private Property Calcular As Object
 
    Private Property TextBoX(ByVal TextBoxCount As Short) As Object
        Get
            Return _textBox
        End Get
        Set(ByVal value As Object)
            _textBox = value
        End Set
    End Property
 
    Public Sub solonumeros(ByRef e As System.Windows.Forms.KeyPressEventArgs)
        ' evitar letras
        If Char.IsDigit(e.KeyChar) Then
            e.Handled = False
        ElseIf Char.IsControl(e.KeyChar) Then
            e.Handled = False
        ElseIf Char.IsSeparator(e.KeyChar) Then
            e.Handled = False
        Else
            e.Handled = True
        End If
 
    End Sub
 
 
    ReadOnly Property Num1 As Int32
        Get
            Return CInt(TextBox1.Text)
        End Get
    End Property
 
    ReadOnly Property Num2 As Int32
        Get
            Return CInt(TextBox2.Text)
        End Get
    End Property
    ReadOnly Property Num3 As Int32
        Get
            Return CInt(TextBox3.Text)
        End Get
    End Property
 
 
    Private Sub Sumar(ByVal sender As Object, ByVal e As EventArgs) Handles Button1.Click
 
        Result1 = {Num1 + 1, Num1 + 2, Num1 + 4, Num1 + 6, Num1 - 4, Num1 - 1} _
                  .Distinct().ToArray ' Elimino duplicados
 
        Result2 = {Num2 + 1, Num2 + 2, Num2 + 3, Num2 - 1, Num2 - 2, Num1 - 3} _
                  .Distinct().ToArray ' Elimino duplicados
 
        Result3 = {Num3 - 1, Num3 - 2, Num3 - 3, Num3 + 2, Num3 + 3, Num3 + 5} _
                  .Distinct().ToArray ' Elimino duplicados
 
        Dim Rand As New Random
        FixedValues =
            (Result1.Concat(Result2).Concat(Result3)).
            Distinct.
            Select(Function(Value As Integer)
                       Return If(Value < MAX, Value, Rand.Next(0, MAX))
                   End Function)
 
        Dim IndexCounter As Integer = FixedValues.First ' 1
        Dim LenCounter As Integer = 0I
 
        Const NumStep As Integer = 5I
        Const NumLen As Integer = 6I
 
        Do Until IndexCounter > FixedValues.Last
 
            Combo = New List(Of Integer)
 
            For Num As Integer = IndexCounter To (FixedValues.Count) Step NumStep
 
                LenCounter += 1I
                Combo.Add(FixedValues(Num - 1I))
 
                If LenCounter >= NumLen Then
                    Exit For
                End If
 
            Next Num
 
            If LenCounter < NumLen Then
 
                For RandomNum As Integer = 1I To (NumLen - LenCounter)
 
                    Dim n As Integer = Randomizer.Next(RandomValues.First, RandomValues.Last)
 
                    Do Until Not Combo.Contains(n)
                        n = Randomizer.Next(RandomValues.First, RandomValues.Last)
                    Loop
 
                    Combo.Add(n)
 
                Next ' RandomNum
 
            End If ' LenCounter < NumLen
 
#If DEBUG Then ' #Debug
            Debug.WriteLine(String.Join(", ", Combo))
            ' Stop
#End If
            Combo.Sort()
            Combos.Add(Combo)
            IndexCounter += 1I
            LenCounter = 0I
 
        Loop ' IndexCounter >= FixedValues.Last
 
        ' ******** ordenamiento-------------
        '  Dim values As Integer() = (From n As Integer In Combos Order By n Ascending).ToArray
 
        ' ********
        ' Listbox:
        ' ********
        Combos.ForEach(Sub(comb As List(Of Integer))
 
                           ' Convierto la Lista a 'String', le añado los ceros, y añado el string formateado al Listbox.
                           ListBox1.Items.Add(String.Join(", ",
                                                          From value As String In comb
                                                          Select If(value.Length = 1I,
                                                                    value.Insert(0I, "0"c),
                                                                    value)))
                           ListBox1.Sorted = True
 
 
 
                       End Sub)
 
    End Sub
 
 
End Class

Solucionado

Combos.Count