The iPhone X was discontinued last year when the Xr and Xs model’s came out. Similarly, the announcement of the iPhone 11 models meant the iPhone XS models were discontinued this month.
The current production lineup of iPhones sold by Apple are the iPhone 11 and 11 Pro, the Xr and the 8, as displayed on Apple’s web site. Also note that the 256Gb versions of the iPhone 8 and Xr have also been discontinued this month.
Apple’s web site always only shows the models they are currently producing and selling. You may see iPhone XS and X models showing up in the Apple refurbished store, if there is a refurbished store on your countries Apple web site (it is not available everywhere).