Miniature 5V Cooling Fan for Raspberry Pi (and Other Computers) : ID 3368 : $3.50 : Adafruit Industries, Unique & fun DIY electronics and kits
how to plug devices using same pins on raspberry pi at the same time? / Raspberry Pi 4 Model B - Stack Overflow
Amazon.com: MakerFocus Raspberry Pi 4B Dual Cooling Fans, Raspberry Pi 4B Heatsink Kit, Raspberry Pi 4B GPIO Expansion Board DC 5V 0.2A with LED Compatible with Raspberry Pi 4B / 3B+ /