In a statement, a Nintendo spokesperson told Eurogamer: "We can confirm that we are no longer manufacturing the Nintendo Classic Mini: Nintendo Entertainment System. If production resumes in the future, an update will be posted on the official Nintendo website."
Although it enjoyed healthy demand and a lack of supply, the NES Classic was never long for this world. Nintendo told IGN last week that the console "wasn't intended to be an ongoing, long-term product" and that the company had already manufactured more units than it ever expected to.
If you're looking to get your hands on one before they sell out, move quickly. Retailers will have limited stock, if any at all. After that, the best place to find one will be on marketplaces like eBay, where Classics are already appearing on the site with significant markups, or you could build one yourself.