The terms “yank” and “seppo” were more common in older generations of Australians. If you could go back to the 1940s, I think you’d hear both terms a lot (in certain informal contexts)

One still occasionally hears “yanks”, but it is quite rare. “Seppos”, one more often hears joking about calling Americans that than anyone actually doing so-and the rare occasions the term is used (as opposed to merely mentioned), are (in my personal experience) self-conscious exercises in derogatory jocularity-related jocular coinages are “Sepponians” and “Seppostanis”

Of course, it is a big country, and terms which have fallen out of general use may be retained or revived in some pockets-I can only describe my own personal experiences