The 3 major BIOS vendors, (AMI, Award, Phoenix) create a base BIOS code for each new revision.
This code needs to be "customized" for each different motherboard configuration. When they create a new revision of the base BIOS code, it is usually toprovide support for new features in motherboard chipsets. This will not provide any "new" features to an existing chipset. The only place to download the "correct" BIOS code for your particular motherboard is from the motherboard / system Mfg.
Unless the motherboard / system mfg. determines that there is a need to revise the BIOS for a particular system, they will not issue a new version. Even when they do, it usually is the same revision of the base BIOS code.
If you believe that an updated BIOS will benefit your system, you can contact Unicore software.
They are a 3rd party company that creates custom BIOS updates for PCs. A BIOS update from Unicore is around $70.
At $70, there are many safer upgrades to improve system performance.