Then when the day comes that the members realize it's more efficient in terms of availability and avoiding future price rises to over-order and keep a running supply of stock available locally, they will have become their own mini-distribution operation.
The only way to stop it would be for the manufacturers to all band together themselves and try to force all of the retail operations in North America (and the rest of the world) to refuse to ever sell anything whatsoever to anyone in Australia. In essence, try to apply a version of the same tactics to individual consumers—or groups of individual consumers—that they do to wholesalers and distributors.
But if the co-op operations eventually constituted a large enough segment of the Australian market—and you've already said that hardly anyone buys film anymore from the officially sanctioned distribution channels—then the manufacturers would have put themselves in the backwards position of trying to force a significant portion of their revenue-producing customer base to NOT buy their products.
And one of the first rules of business is to never put yourself in the position of working against yourself.
(I can see it now. At a future management meeting. "Those Australian buggers have just found a clever new way to get their hands on our products. But not to worry. We're already on it. We'll do whatever it takes to keep our products from ever being sold to, and used by, those guys. They think they're so smart. We'll show them what smart really is...")
Actually, from what I've read here so far, this already doesn't sound too far off the mark.
Why should something like this this work? Because all that's required to make it happen are a few mouse clicks, and UPS delivers worldwide. And it's exactly the same reasons why successful farming co-ops and non-profit credit unions were formed in this country. And both of those institutions continue to flourish here.
You would have simply become your own non-profit mini-version of B&H, using globalization to work for you instead of against you.