When?
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Can you print yourself? I printed this one and I think it is almost perfect: Case for Pi-5 with Pimoroni NVMe Base by OzRocky | Download free STL model | Printables.com
Looks nice but what are those file types? I would need .stl files.
You can convert those 3mf files to stl. There are also online tools like this one: Convert 3MF to STL for free - ImageToStl. This link also explains the differences.
But I am pretty sure your slicer software will support 3mf anyhow, since 3mf is very common. It might not pick up some of the special attributes (e.g. material), but that should be no problem.