Update: individual Arduino Nano Every boards have returned. https://store.arduino.cc/usa/nano-every But the headers are not attached so you have to solder them on, or go the Amazon route which appears to still have them with headers mounted.
Posted in February — It looks like Arduino has discontinued sales of individual Nano Every boards. They are now only sold in 3 or 6 packs, without headers. My guess is that individual boards had too much sales cost overhead, but we may never know for sure because their site is mum about the disappearance, not even listing it as a discontinued product.
Since it really isn’t an introductory board (or at least I don’t consider it one) this might not really make much of a difference. Go ahead and buy three or six of them and add your own headers! Cost is slightly lower than the individual boards once were.