1056k Memory Upgrade Board for the Atari 800 from 5cfab on Tindie
Atari ST Memory Information
Atari 800 48k RAM Card with Jumper Board from 5cfab on Tindie
Amazon.com: Atari Ultimate Arcade Fightstick USB Dual Joystick with Trackball 2 Player Game Controller Powered by Raspberry Pi 3B+ 1GB RAM 32GB Micro SD Card Preloaded Over 100 Classic Atari Games :
Upgrade an Atari 400 to 48K of RAM (1-2 hours) – Atari Projects
Atari 400/800 16K RAM PCB Tested Working In Plastic Case | eBay