It sounds like you're trying to piece together a download for from a third-party site like Apun Ka Games.
You can purchase and download it directly from the Mafia: Definitive Edition Steam page . download-mafia-definitive-edition-apun-kagames-part2-rar
It is also available via the Epic Games Store. It sounds like you're trying to piece together
One-click install—no need to worry about missing .rar parts. download-mafia-definitive-edition-apun-kagames-part2-rar