mileage table

I have a few applications that calculate the mileage from one city or
zipcode to another using the best routes. The main problem I have with
those programs is that I can only enter one city at a time. I am in
need of a table that has all the mileage figured out so I can enter it
into a database and eventually do as hundreds of cities at once. Does
anyone have a table like that or know where I might find one.