There are also some difficulties in Australia. You can get sulfa drugs, tetracycline, and occasionally oxytet or chloramphenicol turns up. I have seen streptomycin once but the price was outrageous. Parasite medications are also a bother because it's hard to find internal parasite meds, the vast majority treat external parasites so there's a lot of dose guessing and finger crossing involved to de-parasite anything. Melafix, bettafix and pimafix are always available along with the standard antifungals, acriflavine, methylene blue, malachite green etc.
The real problem is that nobody knows what these do or how to use them and they are expensive, so most of the time, when Joe Blo's fish get sick, he dumps half a container of whitespot med in the water and when it doesn't work, shrugs his shoulders and sells the tank or replaces the fish. So the medications you can get are usually way, way out of date.
If you want the sophisticated stuff though... basically you have to be a doctor, dentist, vet or nurse, work with one, live with one or suck right up to one. There are backdoor ways of course, but it's a real pain sneaking around the place with bottles of potassium permanganate, copper sulfate and other random chemicals that are sometimes substitutes for decent drugs.