That is blatantly not true. There have been several mass shootings in Australia such as the 2002 Monash University shooting and the 2014 Sydney hostage crisis since Port Arthur, which inspired the modern Australian gun control system. Port Arthur was also 25 years ago, not 35. Australia also only had a handful of mass shootings before Port Arthur; mass shootings have never been a major issue in Australia.
https://en.wikipedia.org/wiki/List_of_massacres_in_Australia