Welcome to the forum Sam and fortunately in Australia, I do not think allergy sufferers are a big proportion of the population, but hayfever can be crucial and even fatal for some.

You do get people generally who might be a bit sneezy with pollen/dust and other airborne particles but that is more a general ailment and not really considered an allergy.

State Health departments may have some sort of records and their sites I would consider an appropriate starting point in researching something like that.