No, Amazon is not a monopoly, they are a very large and influential player. You can still buy eclipse glasses (and practically all other products) from other vendors, both physical and online. It may not be as smooth, cheap, fast or convenient as Amazon, but that's pretty damn far from the bar for a monopoly.

There was never any guarantee that the invisible hand would fix badness overnight, merely that it will nudge them in the right direction. Which it does.