You should be able to restore the 'countries' table in phpMyAdmin.

I have never done this (or something similar) but I would just install another instance of Zen Cart on a sub domain (make sure it's the same version of ZC), then go to phpMyAdmin on that new install and export the 'countries' table to my HD.

Next step would be to back up my live DB and then import the previously exported 'countries' table from my HD into my live DB.

That should restore all your country codes (I hope..... )