I don't think there is much of a "DXM culture" anywhere in Australia, I have known a few people to enjoy a bit of DX here and there but most of them got over it pretty quickly. I only used it twice myself and that was enough to decide it isn't for me, the only way I would use DXM again is if someone close to me wanted to do it for the experience and wanted a tripping buddy.
I don't think there is much of a culture you can associate with DXM, to be honest its a pretty crappy drug and while it is cheap and legal you also get it in a form that just sucks to consume much of.
I have found DXM extremely useful in the potentiation of codeine and for this reason you will seldom catch me without a bottle of Robitussin DX somewhere in my room/drug stash. I think honestly there are much better drugs to be taking than DXM, even in the same class of drugs there is ketamine and nitrous and nitrous is legal to purchase as well. If you like it thats cool, I am not suggesting you stop something you enjoy, but it is my experience DXM is overall not enjoyable enough to get enough people to form a culture around it, unless your maybe talking about a band of dumb highschoolers sipping cough syrup and doing irresponsible things lol. Thats just my opinion.