Hi, I realize this is a late reply but hopefully it can help others if not the OP. I have a z3100PS GP running firmware TR12-TR12PS_7.0.0.3 and still have the original .exe download file. The same file is currently available from the HP support website (
https://support.hp.com/ca-en/drivers), but it's only listed for older OSes. So browse to the z3100 support page, then set the OS to Vista or older (for Windows, sorry I don't know Mac speak). Then firmware options will appear in the list of available downloads. In my case for a z3100ps the file is "TR12-TR12PS_07_00_00-3-2_mvl40-x86-opt_B.exe". It looks like there is a non-ps version there as well.
Although I got that firmware a long time ago, incidentally the above OS-version trick is also how I found the "recent" version of the classic HP Utility and drivers (instead of the crappy default Windows drivers). The PCL3 raster drivers can be found under Win 8 or earlier (as version 61.101.366.41). The same file is listed for earlier OSes so it's a multi-OS package. I tried it on my Win 10 x64 for lack of anything better and it worked fine. The drivers were unsigned tho so Windows blocks the install by default. Have to temporarily disable User Access Control (secpol.msc -> Local Policies -> Security Options -> User Access Control:Run all admins in Admin Approval Mode -> disable) and after reboot then it installed okay. Re-enabled when done. The package also includes the default ICC profiles but you can skip those.
The HP Utility can be found under Win 10 x64 (as version 1.17.0.3, from 2019). Seems to be the last of the "software support" hp gave to these printers.
Cheers
