They mean the Arduino Store:
https://store.arduino.cc/catalogsearch/result/?q=neopixel+ring
I was also a bit confused at first because I hadn't noticed they sold that product in the Arduino store.
I originally had included links to Adafruit and SparkFun product listings in my previous reply but then I noticed that all their WS2812 rings are more densely populated than the ones sold in the Arduino store. So the Adafruit 66 mm ring has 24 WS2812 instead of the 16 on the 70 mm ring in the Arduino store that dan_musci is familiar with. Both densities are sold on eBay and Aliexpress. The links I provided are to the lower density rings like the Arduino store ones.