Does anyone know a supplier that sells the square wood tube amp cases with the metal top for mounting the tube & transformers?

VT4C is one of the few places I've seen anything like what you're talking about, at least recently. There used to be a few other types but they've all disappeared which I'd guess is due to low demand and high prices. I resorted to building my own.

Building your own is highly recommended, even if it take some help from Doctor Wood..

Still pretty, but, fail. Like the old Knack song, "Maybe Tonight".

Not square, but wood:

Welborne Labs Hardwood Chassis

And great prices at Welbourne - IFF they are the right size.

Welborne Labs Hardwood Chassis

Welborne hasn't actually sold those cases in years. I once posted to AA that I was looking for someone to make a few wood cases for me and ended up getting about half a dozen emails of willing builders.