IMPORTANT NOTE: I have
never used this package... and I have no idea how it works... the documentation isn't very good, but there is an "updateFirmware.py" script that appears to load a new Firmware to the device.
Having said that, perhaps you could use the LedgerHQ "Python Loader" package which seems to be capable of updating the firmware:
https://github.com/LedgerHQ/blue-loader-pythonUnfortunately, I have no idea where you can actually get firmware files from. Perhaps try and post on the Ledger Reddit, the Ledger support peeps seem fairly active there:
https://www.reddit.com/r/ledgerwallet/Although it should be noted, that most of their responses to users stuck on firmware 1.2 were to open a support ticket and mention that they were stuck on firmware 1.2.