Do you have the lat/long points for your codes? and when you say equal in distance, what does that mean? equal in distance from the center of the postal code? we need more details to be of much help.
There are example calculations on the community and online to show how to calculate distances between two lat/long points in tableau. I don't think you want to create the distance between every set of points but if you wanted, you could go that route but it has the potential to make a huge data set unless you have a very small number of points.