Amazon.com: Raspberry Pi Compute Module 4 (CM4) - 4GB RAM, 32GB eMMC, 2.4/5.0GHz Wi-Fi & Bluetooth 5.0 (CM4104032) : Electronics
I made the Raspberry Pi 4 with 3GB of RAM. : r/raspberry_pi
Amazon.com: Waveshare Accessory Compatible with Raspberry Pi 4 Model B 4GB RAM with Powerful Processor Faster Networking Support Dual 4K Output and Different Choice of RAM Comes with a Copper Heat Sink :
Raspberry Pi 4 B: How Much RAM Do You Really Need? | Tom's Hardware
The Raspberry Pi 4 gets a RAM upgrade: The 2GB version is now $35 | Ars Technica
Raspberry Pi 400 Gets an 8GB Upgrade — By Hand-Balling and Soldering a Donor RAM Chip - Hackster.io
The Raspberry Pi 4 gets more RAM for $35 | TechCrunch
Assembled Gertboard GPIO Expansion Board For Raspberry Pi
Raspberry Pi 4 Model B With 4gb Ram Bcm2711 Quad Core Cortex-a72 V8 1.5ghz Support 2.4/5.0 Ghz In Stock - Demo Board - AliExpress