These are primarily promoted outside North America, so you might have to use a European or South American Amex site. The lounges are not as extensive as the Diners network. Some are actually operated by Amex, others are affiliates and the same as the PP and Diners lounges, generally third party non-airline airport lounges at major international/non-North American terminals.

The one I am most familiar with is at EZE, just by the gate used by AC -- who sends its J customers way down the terminal to the RCC -- in the new international terminal. However, I have used affiliate third-party lounge at JNB which had both the Diners and Amex logos on it. (However, I believe they restricted access to SAfrican-based Amex cardmembers.)