Because of the legal nature of ROM files, they are not hosted on official GitHub repositories or documentation pages. However, the community maintains "Reference Sets" on archival sites. To find the most reliable links, you should search for:
Alternative Eightiesmod Build : A large collection (approx. 13.7 GB) that includes parent ROMs and some samples. Understanding "Full Non-Merged" Sets mame 2003plus reference full nonmerged romsets link
You can find pre-built versions of this collection or the tools to build them yourself at the following authoritative sources: Because of the legal nature of ROM files,