In the older days of fish chats I knew a few fish keepers down under. I was always imprssed by how they had overcome, legally, some of yor most restrivie imporation laws to acquire fish. his involved finding breeders there.
I can only speak for places in the States. I do not know how available some of what I discus are I australia. But I would imagine some of them are in some form.
As for the advice you don't want to hear, never forget that stores exist to sell stuff and not to turn away sales, This applies even if it is live fish related. Your best weapon is to do some independent research before you buy.
I set up my first tank in Jan 2001. Today I am about to retire having bred rare plecos and sold them to fish keepers across the country. I have worked with people who imported and gotten fish that way. I have bought fish at my club's auction at the end of each month's meeting. I have bought most of my fish shipped in and almost never from stores.
I do not trust the fish departments of larger pet stores. I might trust some dedicated fish stores, but very few. There is one about 30 minutes from me. Their prices are pretty high and their fish are pretty healthy and the knowledge of any employee is quite high. I would trade some of my fish to them for store credit to spend at their retail price. I know that to get a job there you are required to pass a rather intensive written test on an assortment of fish and related matters from meds to plants. Back when the less pricey tetras at a pet store sold for $2.50 or so, theirs sold for $4.50.
Next, there are younger hobbyists who would be in the age range that PetCo and PetSmart hire who also happen to be a serious fish keepers and who have more motivation to work in these places in the fish dept. than most. So you can occasionally bump into such a person. but do not hold your breath....
Two of the best sources for information are a local fish club and most weekend fish events. Most of these are sponsored and run by fish clubs because the members are working for free. The other thing is over the years of attending such weekend event I have met and talked with people like Ingo Seidel, Hass-Georg Evers, Leandro Sousa, Julian Dignall aka Jools of Planetcatfish, Rachel O'Leary, Barbie Fiorentino, Stephan Tanner, Shane Linder and the list goes on. I never imagined some of these folks would bother to talk to me. I have learned things from every one of them I might never have known otherwise. (My apologies whomever this old brain may be forgetting to name here.) I am not including any of the folks with whom I have only chatted or exchanged Emails with but have never met.
My point is, all one has to have is the curiosity to want to know the most accurate answer to our fish related questions. The challenge then becomes learning where and how to find that information. The odds are, when looking online, one will find more poor information than good. I am considered, in some circles, to be a respected breeder of a narrow group of B&W Hypancistrus plecos. However, I could not come close to passing the test to work in the fish pet store I mentioned above.
Here is the best advice I can give you. Join a local fish club if you can. Learn about any fish events you can attend that might be in any way of interest. All of us were beginners at some point.
Online here is a little headstart with 2 good sites. I hope others can add a few more for you.
You can get a head start on fish species info, go here
https://seriouslyfish.com/
For catfish, go here
https://www.planetcatfish.com/index.php