As Socket54 suggested, there are a few sites that maintain databases of the original "clean" ROMS just for such an occasion. One I have used is TechPowerUp. You can change the query to match your specific card, but here is a start for your Sapphire 470's: https://www.techpowerup.com/vgabios/?architecture=&manufacturer=Sapphire&model=RX+470&interface=&memType=&memSize=4096&since=

As suggested earlier, the first thing you need to do is get all the cards working again with a stock BIOS and default speeds/settings before looking around for another modified BIOS.