Sorry I can't really answer specifics about Australia, but we have a number of Aussie members who I hope will be able to help.
From my understanding - (hope to be corrected if I'm wrong) - you are right that though allowed, in general bite-sports are seen in a very negative view in Australia. There are IPO clubs, but probably very few of them, and the vast distances less-developed interior territories might make it hard to find a club anywhere near - (I can relate to vast distances and less-developed territories - for example, the nearest large city to my town is an 8+ hour drive through the rockies).
The way to get started is to find a club and to join. Best thing is for people to join even before they have a dog, learn from watching and helping, and use the experience and resources of the club to help find a suitable pup for the sport. Reality is that most people join with the the dog they already have, which can be a mixed breed or an other breed, learn as much as they can, go as far as their existing dog has the potential to go, have a blast during the whole process, have their mind's open up to a whole new way of understanding dogs, dog behaviour, and dog training, THEN after a year or several, go and get a more suitable dog of working lines to work with.
Most clubs meet at least one day for the full day on the weekend, and once or twice more during the week, in the evening. Clubs have different personalities and goals - some clubs are very competitive, expect their members to participate fully and have a dog that is competitive and has the potential to make it to high-level trials, while others are more laid-back, more of a social club, more about getting together and working together and having fun, with more modest expectations and goals.
I'm not sure what you mean by
Can only certain types of people participate?
Usually having an interest, having a dog, and getting along well with others is what we look for in new members.