I had recently purchased a Wico A5200 Controller with the splitter cable, but was unable to locate the Keypad.
So, browsing the Internet I procurred these 3 parts:
Cable: https://console5.com/store/neo-geo-aes-atari-5200-pc-controller-joystick-repair-project-cables-4-1-2m.html Keypad: https://www.ebay.com/itm/253937062984 Mounting Box: https://www.ebay.com/itm/Ham-Radio-CB-Project-Box-Enclosure-Black-Plastic-1-X-2-5-X-3/163463229370?hash=item260f2aefba:g:kzkAAOSwSatbF0hf:rk:9:pf:0
After some drilling, soldering and some Plumber's Goop, I came up with this.
Sure, it's a "Frankenstein", but it works!