That's exactly what I said - the only mentions that now exist are on forums asking questions (does it work, where can I find it etc). With no official source for the file.
Whether the BIOS was developed by ASRock, AMI or a third party BIOS community, it doesn't matter.
TODAY, the only sources for these files are of unknown reliability.
The claim is certainly that the rumoured 2.39 supports the chips you want... and logically, the board uses an AM2 socket and does support >100W CPUs (just not the Phenoms officially), so a ~125W AM2+ CPU is not out of the realm of possibility... in theory.
Consider though, if it never made it beyond beta stage, there may well have been a problem (stability, compatibility)... If you encounter said issues, what would you do?
In practice, to source the file you'd have to be prepared to download from some questionable corners of the internet AND then flash said questionably obtained file to the BIOS chip of your motherboard.
In a perfect world, it would be a legit BIOS and just 'work', with no ill effects.
In the real world, at best it's likely unstable and difficult/impossible to downgrade....... at worst, the sites/users who continue to host the file have injected malware (or worse) which then applies at a BIOS level.
If it doesn't just "work" perfectly (unlikely, or it would've been a release BIOS).... chances are you'll have a board that's no longer fit for purpose for one reason or another.