Compucase used to have loads of models like that, in example LX6A21. Maybe search those on ebay/craigslist/whatever you happen to have around? I have couple of those laying around, but I assume shipping from Finland would be stupidly high for a 10+ year old case. Or, as you said, pretty much any older tower would be a good option. But as they’re just sheet metal and plastic used ones are just fine. You might not get USB3 on the front panel, but as it’s a server does it really matter?