Так нужно?

Private Sub UserForm_Initialize()
    ar = Range("Таблица2[Столбец5]")
    Set slov = CreateObject("Scripting.Dictionary")
    With slov
        For i = 1 To UBound(ar)
            If ar(i, 1) <> "" Then
                If Not .Exists(ar(i, 1)) Then
                    UserForm1.ComboBox1.AddItem ar(i, 1)
                    aaa = .Item(ar(i, 1))
                End If
            End If
        Next i
    End With
End Sub

Sub fffff()
    Dim ar, i
    With UserForm1
        .ComboBox2.Clear
        cb1_ = .ComboBox1.Value
        If cb1_ = "" Then Exit Sub
        ar = Range("Таблица2[[Столбец5]:[Столбец6]]")
        Set slov = CreateObject("Scripting.Dictionary")
        With slov
        For i = 1 To UBound(ar)
            If ar(i, 1) = cb1_ Then
                If Not .Exists(ar(i, 2)) Then
                UserForm1.ComboBox2.AddItem ar(i, 2)
                aaa = .Item(ar(i, 2))
                End If
            End If
        Next i
        End With
    End With
End Sub

CreateObject("Scripting.Dictionary")

Private Sub UserForm_Initialize()
    Application.ScreenUpdating = 0
    Application.Calculation = xlCalculationManual
    ar0 = Range("Таблица2")
    With ActiveSheet.ListObjects("Таблица2").Sort
        .SortFields.Clear
        .SortFields.Add Key:=Range("Таблица2[[#All],[Столбец5]]")
        .Apply
    End With
    ar = Range("Таблица2[Столбец5]")
    Range("Таблица2") = ar0
    Application.Calculation = xlCalculationAutomatic
    Application.ScreenUpdating = 1
    Set slov = CreateObject("Scripting.Dictionary")
    With slov
        For i = 1 To UBound(ar)
            If ar(i, 1) <> "" Then
                If Not .Exists(ar(i, 1)) Then
                    UserForm1.ComboBox1.AddItem ar(i, 1)
                    aaa = .Item(ar(i, 1))
                End If
            End If
        Next i
    End With
End Sub