I'm facing the same problem. I think it has been many years since VDO made the square bezels. I think it's time to replace them with something new. I have a couple of bad gauges so I think I'm just going to treat myself to a couple of new instrument panels.
Hop, As you probably know, the square bezels were an option (twist- fit) on some VDO round gauges. Google suggests they are still available at around $4.50 each. On the other hand, new gauges are rather nice!