First of all, for information, you can know what BIOS was injected in the factory for your motherboard by looking at the last 4 digits of the label at the top right of your motherboard :
Then, the first available BIOS on the support page of your motherboard is 0701, but before that, there were 2 known pre-release BIOS that are the 0505 BIOS then 0604 BIOS (two are unavailable for download) :
0505 BIOS :
0604 BIOS :
But just out of curiosity, why are you looking for these pre-release BIOS ?