You can find the latest firmware on the HP Support Page for the 6300 SFF and Microtower models.
Official BIOS files are rarely distributed as standalone .bin files on support sites. Instead, they are packaged within executable ( .exe ) files. hp compaq pro 6300 bios bin file
To get the raw binary, download the SoftPaq (e.g., sp73099.exe for v2.99 or sp95971.exe for v3.08) and use a tool like 7-Zip to extract the contents. You can find the latest firmware on the