Rather than searching for the individual file, look for a "MAME Bios Pack" or a "System 16 Device Set." These usually include all necessary decryption keys.
If you own the original arcade PCB for that game, you can dump your own EPROMs using an EPROM programmer (e.g., TL866, MiniPro) and the mame -romident tool to verify the dump. Epr-18022.ic2 Mame Download