Evercase seem to sell some very dated designs, though who knows if there's any stock left: https://www.evercase.co.uk/index.php?route=product/category&path=63

There's also this novelty case from Silverstone, but it's more "retro-inspired" than a true oldschool case: https://www.silverstonetek.com/en/product/info/computer-chassis/flp01/