Apple might have discontinued the iPhone X, 6s, and SE, but that doesn't mean you can't still get your hands on them. This isn't some kind of secret sale, but just a matter of purchasing such discontinued models from your preferred wireless carrier.
If you live in the United States, the four major U.S. wireless carriers are offering deals on older generation iPhones that include not only the iPhone X, 6s, and SE - but also the iPhone 6s Plus.
If you're a customer on T-Mobile, the carrier is currently offering the iPhone X priced at $899, while the iPhone 6s is priced at $449, and the iPhone SE is down to $349. AT&T is also currently offering the same deals, charging $899 for the iPhone X, $449 for the iPhone 6s, and $349 for the iPhone SE. If you're looking for more storage, AT&T offers options, but T-Mobile will only have the base options available.
As for Verizon, they offer different storage options for the iPhone X, as well as the iPhone 6s, with the former starting at $899, while the latter will cost you $449. Sprint is also offering the same deals for the iPhone X, iPhone 6s, and iPhone SE. These are just some of the options that are available, with smaller wireless carriers also having their own deals. If you were looking to upgrade or buy one of these handsets, wireless carriers could be a great alternative to the used marketplace.