I thought there were plenty of those available freely.

Are these good enough? :

http://geocoder.ca/?freedata=1

US Zip Codes

File of all US 5-digit ZIP codes. Includes zip, city, state, latitude, longitude, and county (Last Updated: March 30th 2010):

US Zip Codes (41,755)

or

http://sourceforge.net/projects/zips/

Edit: MaxMind recommends this one

http://download.geonames.org/export/zip/

There's also Google's geocoding API.

Still, let's hope the project owners answer you :)