https://www.gamespot.com/articles/snes-classic-edition-guide-how-to-buy-one-at-relea/1100-6451207/

September 28: The SNES Classic Edition's release is finally upon us. Fortunately, it looks as if you'll have an opportunity to purchase one on launch day (September 29) even if you weren't able to secure a pre-order. Nintendo has urged fans not to pay more than retail price and announced plans to extend availability into 2018 (it was originally only supposed to ship during 2017). But even on launch day, at least some stores will have them in stock.

September 12: While pre-orders themselves may not be any easier to get, Nintendo has provided some encouraging news for those hoping to purchase an SNES Classic Edition. Nintendo of America president Reggie Fils-Aime recently implored people not to pay more than regular price for the console. Now, the company has announced that the SNES Classic will continue to be sold into 2018, and not just in 2017 as previously planned. (The NES Classic is also coming back.) On launch day in the US specifically, Nintendo said that "more units of Super NES Classic Edition will ship ... than were shipped of NES Classic Edition all last year, with subsequent shipments arriving in stores regularly." This is still no guarantee that you'll easily get one, but things are looking better now than they did.