You can literally buy a small device and flash the trezor firmware on that device etc I have seen an article somewhere about the steps a guy has taken to install trezor-firmware on his own made hardware wallet.
The case doesn't have to look the same as the one for Trezor, but if you want to assimilate the looks of a Trezor One, you can follow the guide that dkbit98 mentioned in his thread
Make your own Trezor Hardware wallet for under $40. Whether or not all the spare parts are still around for under $40, considering the inflation and the general chip shortage, is a topic for a different discussion.