Here are the most requested BIOS files and their exact required filenames for MAME.
You can check if your BIOS files are valid using MAME's internal tools. bios mame
Move the BIOS zip files into your primary roms folder. Unlike games, BIOS files must be in the main ROM directory (or a directory specified in your mame.ini file) so the emulator can find them when you launch any associated game. Here are the most requested BIOS files and