A Futaba MD PCB for TI-99/4a
Included is also a simple Arduino sketch for testing the keyboard. Connect the rows (pin 8,13,14,15,9,12 on the connector) to port C, the columns (pin 5, 4, 1, 2, 11, 3, 10, 7 on the connector) to port A, and pin 6 on the connector (ALPHA LOCK) to A0. You may have to experiment with the pin numbering; I can't verify the order.