Each half consists of a bottom and a top part (with an integrated switchplate) and is meant to be 3D printed in resin.
I got good results from JLCPCB (15€ + tax and shipping for a black or white version) and PCBway (50€ + tax and shipping for a clear case).
Where possible use the STEP files, but the STL files should be fine too.
If you're sure you only will use the wired version you can also use the case without a power switch (USB) or use the case without a TRRS cutout if you plan on using the wireless version (BLE).
Note The manufacturer will probably warn you about too thin sections, but it worked fine for me since these sections are pretty small.
