Part of what makes these slightly hard to find, I think, is the rarity of the sockets. The NES is now over forty years old and I doubt anyone's caused a factory to produce more parts for them since at least the year 2000, so anyone making commercial adapters will be doing so in very small quantities.

Mayflash, for example, seem to have given up on that approach entirely, and their adapter uses a 9-pin connector and (I suspect) a butchered extension cable to make it work: https://www.mayflash.com/product/PC053.html

So, the goal for this mini project will be an Arduino 32U4-based adapter with a couple of 3D printed NES controller sockets on it. That could be replicated for well under AU$10 by someone with the right machinery and skills if someone (I'm the someone!) wants to burn some spare time in making a design that will work, and most of that cost is in the Arduino-compatible board - the rest is cents of plastic.

Worst case, I'll build a few with the official sockets, and make those available too.

It'll be weeks before I have any electronic parts to play with, but for now I have a 3D printed socket that perfectly fits the plug on one of my NES controllers. A 0.4mm nozzle isn't fine enough to print walls between the pin shrouds in the connector, so my version will look open like this.

Do you have a 3D printer, a NES controller and half an hour to kill? DM me, I'd love to test this part on other printers and with other random controllers people have in the cupboard.

#3DPrinting

@ireneista oh, that's interesting. Do you know what games those might have been?

I do plan to pick up a light gun at some point just to test detecting its inputs using those extra pins. If there's a game I could try on an emulator, that'd be an awesome proof-of-concept for my adapter.

@timixretroplays based on our watch history there's a fair chance it was a passing mention in https://www.youtube.com/watch?v=keyDD-Eqom0

we sure wish youtube's transcripts were searchable, or even skimmable