With all those naval forces you have around Bataan, Singapore, and Port Morsby you'd think they couldn't get any supply in there. Naval forces should cut off supply to a hex if you have it completely locked in by land and by sea. Sure would make taking those places easier if they were out of supply, but I don't believe there are any rules for naval blockades but maybe they could put it on the wish list?
Doing something like that would require more extensive changes to the supply model. At a minimum you'd need to differentiate between blockadable supply points and those that represent pre-existing stockpiles that should continue to be available even if the line of supply to the rear is interrupted. Some of this can already be done by adding/removing supply points using the event system. Doing so is easier in single battle scenarios where Turn N is a suitable trigger. IN more open ended ones where more flexible triggers are needed and being able to break a blockade and restore supply can use up a lot of events depending on how complex a situation you want. There may also be issues with hitting the maximum allowed number of events. I know a lot of big scenarios maxed out the count in ACOW, IIRC the max has been raised in newer version but am not sure if it's still reachable by ambitious designers.
Did you ever see history portrayed as an old man ... weighing all things in the balance of reason?
Is not [it] an eternal, imploring maiden, full of fire, with a burning heart and flaming soul, humanly warm and humanly beautiful?