Use isso
Option Explicit
Public Sub Button1_Click()
Const RNG = "B2:B600" '<--- Range on Sheet1 --------------------
Const OFFSET_ROW = 2
Const START_ROW = 10 '<--- Start row --------------------------
Dim ws1 As Worksheet: Set ws1 = ThisWorkbook.Worksheets("Sheet1")
Dim ws2 As Worksheet: Set ws2 = ThisWorkbook.Worksheets("Sheet2")
Dim r As Long, ws2val As String
ws1.Range(RNG).ClearContents
For r = START_ROW To 30 * OFFSET_ROW + START_ROW - 1 Step OFFSET_ROW
ws2val = ws2.Cells(Application.RoundUp(Rnd() * 88, 0), "A").Value
If Application.CountIf(ws1.Range(RNG), ws2val) = 0 Then
ws1.Range("B" & r).Value = ws2val
Else
r = r - OFFSET_ROW
End If
Next
End Sub
Dados de teste em Folha2 e Resultado em Folha1 em (Saída começa na linha 10 como você pretendia)