It appears Apple has discontinued the iPhone 7 and iPhone 7 Plus with 256GB, and it also seems Apple no longer offers (PRODUCT) RED special edition items as well.
Apple seems to be making some changes in its handset device area just before the release of the iPhone X, it seems Apple has discontinued the iPhone 7 and iPhone 7 Plus with 256GB. This transition seems to have taken place during the launching of the iPhone 8 series, and the introduction of the iPhone X. Some believe Apple made this change to give the iPhone 8 series more of a chance to move into the spotlight.
Another possible permanent discontinued product is (PRODUCT) RED special edition items, it seems Apple has removed some of the (PRODUCT) RED products from its website.
If you are still interested in buying either the iPhone 7, iPhone 7 Plus with the 256GB or the (PRODUCT) RED edition products you may want to try Amazon, eBay or another reputable third-party for these particular items while supplies last.