Testosterone is a restricted substance, so can't be purchased (legally) without a script.
Some GPs are willing to provide prescriptions for T, even in the absence of low testosterone levels (on an informed consent approach).
I'd advocate it's a safer way to go if you can find such a doc, as this way you can also have them monitor your levels through regular blood tests (as well as keeping an eye on signs for possible adverse effects on the liver, cholesterol, and RBC count).
Testosterone has both androgenic and anabolic effects. The anabolic effect of testosterone is to enhance protein synthesis and muscle growth. The androgenic effect maintains masculine traits such as voice, hair distribution and fertility. For testosterone, the androgenic and anabolic effect are about equal 1:1.
Bodybuilders will use synthetic anabolics that have a much higher anabolic effect than testosterone. Anadrol (Oxymetholone) has an androgenic anabolic ratio of 1:3..Anadrol is one of the most potent anabolic steroids available.
The older oral synthetic steroids tend to be more toxic to the liver. That is one reason that injectables are used.
I don't know the regulations in Australia. In the US, a physician can get into trouble if he prescribes testosterone or growth hormone to an individual that does not have laboratory evidence of a deficiency. Synthetic anabolics should only be prescribed for wasting disorders like AIDS or metastatic cancer.
Sorry..I have no idea where you can obtain anabolics illegally.