I don’t know any mafia-specific VC fics out there… 😛

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“Gorgeous…vamps?“ by Endymiasyzygy]

The only fic that comes to mind is 

The Hostile Takeover by StellaMachiavelli (@stellamachiavelliici​):

Lestat de Lioncourt is a high-flying businessman out for revenge on ruthless boss Santino, with the help of his best friend David Talbot. There’s just one complication: on Santino’s side is Lestat’s ex, Louis de Pointe du Lac.

…but I don’t remember if it’s mafia-related or all legal business.