Are you certain it's not already drilled and tapped?
The holes will have hard plastic plugs in them and may not be readily visible.
The factory Novas are patterned for the 423M base, but if it's not already there, I'd have it done in the Remington 700 or another more common pattern.
That way, finding a decent rail to fit it won't be a problem.
The gun dealers you asked are dolts. If Benelli offers it with factory drilled and tapped receivers, then it only stands to reason that it can be drilled and tapped.