I have the same article and no, there are no references. Dr. Korfmann was a German archeologist who spent major amounts of time at the Troy site. He also wrote a book on the comparisons of the bow and sling from the site of Troy. Alas, I have found the book, but it is totally in German. There is no english translation that i have been able to track down.
He does cite some original authors from the timeperiod. Those are easily looked up. Infact, I am also writing a research paper on slings, and have followed this path. He cites only a small amount of what is available, especially from Vegetius.
Given his credentials, I would think that he could be a primary source.