@mjdxp
I own two "3.5 USB drives and I've never seen a "5.25 one, maybe you can find a converter-controller and an old drive separately, but I don't even recall the name of the interface those used for connection 🤔
@mjdxp That's odd, but it's probably because they were much more fragile than 3.5 ones, the mechanical parts and even the connector — it was just a side of a circuit board, similar to what we have today on PCI expansion cards, those are prone to breaking and considering how long ago those were produced, few might have survived 😔