Решение на другом форуме мне подсказал Shaidar Haran.
Code:
LastFolder = ""
Set FSO = CreateObject("Scripting.FileSystemObject")
Set Folder = FSO.GetFolder("C:\Temp")
For Each SubFolder In Folder.SubFolders
If IsNumeric(SubFolder.Name) Then
If (SubFolder.Name > LastFolder) Then LastFolder = SubFolder.Name
End If
Next