NHC Projected Half Yearly Dividend, page-291

Directors have to report their share purchases to the ASX.
There is no "source" because they have never bought shares just before the Company is due to announce their result.
The ONLY time the Milner's and other Directors have bought shares is after the Company announces it's Financial result and details of the Dividend are declared. They may well buy after the announcement, but before the shares go ex the dividend. At that point the market has the same performance information as the Directors.
To do otherwise is insider trading, illegal, and they would likely be in jail.