I sure wish there was an easier way to do it. Even if you had the rates in a table, you can only paste them down under the weight column, and not across the state row. Also, when (not if) USPS increases their rates, we get to do this all over again!
I have downloaded the USPS zone charts and the weight charts. Then I had to look up the zip codes for each state and figure out their zone. I put all of that information in a table to work with. I wanted to do this for both Priority Mail and Parcel Post, which means a really lot of work. This is really taking a bite out of my time.
I found a shipping calculator and wish that I could use it some how. It's called PaidAuction, and has remarkable functionality. There is a free and paid version. Perhaps CC would consider integrating their shipping calculator into future Shopping Cart Creator Pro's updates.
One thing you might want to consider is just using Zone 6 or 7 for everybody. You will be overcharging for some, and losing on others, but maybe it will average out.