It's not only scalpers who pick these up, there are literally thousands of Zelda fans world wide, and this is one of the first actual collectors editions available for it and for a new system at that, bound to be sold out.
But yes, using page monitor alerts through web browsers, signing up for mobile alerts via multiple and various related twitter accounts, apps with instant notifications such as WeChat and WhatsApp etc, and frequenting many forums are all ways that those who are interested in acquiring ANYTHING of limited availability (i.e. Amiibo) do it. There's also using past behavioral analysis such as the fact Amazon.com typically seems to do resets and updates ~0000-0100PST, and other knowledge regarding other retailers online behavior (or "inside info" via Reddit groups and such) also help those who are looking. I'm not a "scalper", but these are some of the tools any savvy fan needs to use to acquire certain limited items sans paying eBay bloated prices or having extremely good "luck".
Hope that helps you in your search... unless you're a scalper in training, then forget everything I said. In that case, they usually download all sorts of amazing tools and cd-key crackers and full length movies via torrents and such to help them... don't worry, those alerts about malware are all fake!
