That's almost impossible. Mafias spring up among groups that require protection due to disenfranchisement or outright negligence by local authorities. Since Germans rarely faced this sort of discrimination in the US (unless they were Catholic), the need for a "mafia" never emerged.
Sicilians and Jews, on the other hand, tended to bring mafia systems over from the Old Country and continue the practice here since they were minorities that tended to be targeted/exploited/ignored by the preexisting Irish city machines that bore no particular love for "sheenies" or "guineas."