not necessarily gun shows of course, that's just where it's easy to find private sellers - private sales don't require background checks
Kind of undercuts the whole some states have really good gun laws argument.
It's moot when the inter state borders are leaky - the genius of Australia wasn't that guns were banned (they weren't) but that national gun laws were unified across all states so that all sales are registered and all buyers are vetted for criminal | domestic violence backgrounds.