Okay checked some details. Marcellus was in command of the fleet at Ostia and he dispatched a legion equivalent to Teanum Sidicinium thus covering the bridge across the Volturnus and blocking the southern route to Rome.
Rome itself he sent some 1,500 reinforcements to. The city already had two legions stationed there and in addition the Senate started an emergency recruitment program to raise four more plus allies troops, further they armed 8,000 volunteer slaves and 6,000 prisoners though there may have been something of a shortage of arms for all this as they had to raid the temples. In addition in an emergency there was a legion in Sardinia and two in Sicily that could have been brought in by sea.
Oh and Hiero of Syracuse sent gold, plus shiploads of wheat and barley (even more useful in resisting siege than gold) and 1,000 archers to Rome.