I use raspberry pi running retropie and have many official controllers converted to play every console. However I can’t find one for turbografx to USB adapter.
I found one for circuit, but I would like to buy one built.

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USB adapter only~

The protocol is pretty simple (basically a Genesis 3-button with turbo and a different connector). You only need five signals, so a basic ATtiny85 doing bit-banged USB could do it (something like the Digispark). Sourcing the DIN jack to save the cable is going to inflate the BoM cost by a large margin, though. You should just detach the original cable and stick the USB stuff inside the pad (if there’s room).

I just use an SNES or Dualshock pad for everything 😛

An adapter is finally available for this project. It just took an extra step since I had to convert the Turbo to a PC engine

https://www.ebay.com/itm/US-Turbo-Grafx-to-Pc-Engine-console-game-pad-Adapter-cable-Brand-New/112897134057?hash=item1a49318de9:g:yTQAAOSwo0JWK8wW

http://www.raphnet-tech.com/products/pc_engine_to_usb_adapter/index.php