Tell the world you are blockading Taiwan and any ship entering or leaving their territorial waters will be sunk.  Any nation that sends a ship into the blockade zone is considered hostile and will sunk without warning.  Once the insurance companies and IMO hear that nobodies ships will service Taiwan.  Perfectly legal to do in the context of a war.  It would then fall to the navies of the US, Taiwan and any allies who cared to join to escort willing ships through the blockade.  The US could buy surplus ships and put them under the US flag.