You can buy the Air Quality Kit for Raspberry Pi directly from the following retailers.
The MonkMakes Air Quality Kit for Raspberry Pi is based around the MonkMakes Air Quality Sensor board. This add-on for the Raspberry Pi measures the quality of the air in a room (how stale the air is) as well as the temperature. The board has a display of six LEDs that display the air quality and a buzzer. Temperature and air quality readings can be read by your Raspberry Pi, and the buzzer and LED display can also be controlled from it.
The Air Quality Sensor board, plugs directly into the back of a Raspberry Pi 400, but, can also be used with other models of Raspberry Pi, using the jumper wires and GPIO template included in the kit.