I would dedicate a table to Ports of Lading. There are international standards for naming ports. Maybe you can incorporate a standard that works for your business.
http://www.page-int.com/?p=pages/res...ign-port-codes
When you enter data into your DB, you can use a combobox and store the Primary Key in relative tables like Purchase Order, etc. Using controls like list boxes and combobox's helps to insure integrity of relations.
Then, when you look at a client's activity you can see a standardized description of the Port. The link I showed you has numbers that are unique to each port. I would still use an Autonumber field as the DB's primary key and have additional columns for the Name and Port Code.
Also, there should be paperwork that has a master or house bill that will describe the relevant port. Make sure you are using an authoritative source for data before you store it in your DB.