[Matt R.]

Hi,
I'm not an atheist, but axioms are so basic and obvious that they are self-evident. Thus, they require no proof. As for where an atheist believes these axioms come from... they simply exist due to the necessity that our reality is logical. i.e. our universe has always existed or came into existence by random occurence, and since our universe is based on logic, basic axioms must hold.

I'm not sure this is the best explanation, but basically I am saying that because our universe is logical by its very nature, then the basic axioms which follow naturally from logic have "existed" since the inception of the universe.