The old Bofors 40/L60 is long out of production, true, but its successor the L70 is alive and well:
Oto-Melara Twin Forty Compact. It's arguably a better choice than its bigger half-brother, the Mk.110 57mm (Bofors 57mm Mk.3), owing to a higher rate-of-fire and better ammunition capacity, but OTOH the Mk.110 is already in USN service.
Of course, this is all assuming that upgrading Arizona is going to be that easy, cheap, or painless. Would demetrious let the questers get away with something that easily and cheaply? Even if he does allow something like this, what's he going to make it
cost? (And I don't just mean in terms of time, money and material....)