I do not remember anyone mentioning this source of retrofits and retro-kits: https://thebrewingacademy.com/ for example: https://thebrewingacademy.com/products/texas-instruments-99-4a-flashrom-99 The Brewing Academy FR99: FlashROM 99 Cartridge for the Texas Instruments 99/4a $34.99 The Flash ROM Cartridge for Texas Instrument 99/4a , or FlashROM 99 for short, is a cartridge for the TI 99/4A home computer that allows for running ROM cartridge images stored on an SD card. The FlashROM 99 supports ROM-only images of up to 32K that use the write-to->60xx bank switching scheme. It will not work with programs using GROMs or CRU-based bank switching. The cartridge does not require the Peripheral Expansion Box and runs on both PAL and NTSC consoles. Apologies if this was already known. -- jeff jonas