OK - I think the following changes should do it

Public Sub saveAttachtoDisk_VendorB(itm As Outlook.MailItem)
Dim objAtt As Outlook.Attachment
Const saveFolder As String = "S:\Test\"
Const saveFolder2 As String = "C:\Path\" 'The second folder
Dim strExt As String
Dim strName As String
    For Each objAtt In itm.Attachments
        strExt = Mid$(LCase(objAtt.Filename), InStrRev(LCase(objAtt.Filename), Chr(46)) + 1)
        strName = "Vendor" & strExt
        strName = FileNameUnique(saveFolder, strName, strExt)
        objAtt.SaveAsFile saveFolder & strName
        strName = FileNameUnique(saveFolder2, strName, strExt) 'Check the second folder
        objAtt.SaveAsFile saveFolder2 & strName 'Save again in the second folder
    Next objAtt
lbl_Exit:
    Set objAtt = Nothing
    Exit Sub
End Sub