Chris, are you saying God quit speaking after the 12 died off? Seriously, at what level do you want to have this conversation? Has God said anything to anyone since the first century?
God does not speak to everyone to the same level. Numbers 12 comes to mind. Miriam and Aaron were severly rebuked and Moses writes large portions of scripture.
It seems to me that he spoke to the Apostles to another level than he speaks to you and me. The twelve walked the earth with him and lived with him. Paui encountered Jesus on the road to Damascus. Paul tells us in 2 Cor 12 that his encounter with Jesus was more than "Nice to meet you. Sorry about the whole persecution thing.".
The twelve did not have to justify their apostleships but Paul did, and the thing that he seems to keep coming back to is the personal contact with Jesus and the fact that he recieved the Gospel directly from Jesus and not from any man.
Paul might be suspect since he was not one of the twelve, but Peter confirms him and even refers to Paul's writings as scripture. The apostles were authority figures.
Now moving on to the last 2000 years or so. Those who have since claimed to be apostles in authority in either word or deed to my knowledge have all been false. I have already listed Muhhamad and Joseph Smith, etc. If you have a different answer to this presumably you would not be here.
So lets look at the leaders, the pillars of the Christian faith for the last 2000 years? Who are they? Augustine, Luther, Calvin, Wesley, Edwards, Whitfield, Moody, Barth, Graham to only name a few? To my knowledge not one of them claimed to be an apostle or claimed to have any apostolic authority. Any authority they had rested on scriptures and to my knowledge they themselves would not claim otherwise.
So like it or not that is where we are today.
I am open to other views, but so far no one has been able to say who might the other apostles be and what they taught?