Your source offers US (and Canadian) postal code data as of May 2011, including lat/lon for USD79.95.

The project description sounds like a graduate level (PhD dissertation?) project. If this is indeed that, or, in fact, other than a self-funded project, one might think that a reasonable budget would include that kind of allowance for data acquisition.

If it doesn't, /methinks one would still * NOT * be entitled to steal data.