Raspberry Pi 4 11mm Embedded Heatsink (P165-B) – Geekworm
Amazon.com: GeeekPi Raspberry Pi 4 Heatsink, 20PCS Raspberry Pi Aluminum Heatsinks with Thermal Conductive Adhesive Tape for Raspberry Pi 4 Model B (Raspberry Pi Board is Not Included) : Electronics
Copper / Aluminum Heat Sink Kit for Raspberry Pi - Micro Connectors, Inc.