Given the legal gray area, major ROM sites have largely been taken down. However, the Mame 0.139u1 Bios Pack is still preserved in archival projects like the Internet Archive (search for "MAME 0.139u1 ROMset (split)").
Safety tips:
Without a proper BIOS pack, these games will either refuse to boot or get stuck on a black screen. The MAME 0.139u1 BIOS Pack contains all these motherboard firmwares in one consolidated download. Mame 0.139u1 Bios Pack
Despite being over a decade old, MAME 0.139u1 holds a special place in the emulation community for several reasons: Given the legal gray area, major ROM sites
Because you are using an older version, modern BIOS files will not work. The MAME development team frequently renames ROMs inside BIOS packs to match new discoveries about the original hardware. Given the legal gray area