I have a bunch of Gadgeteer modules from long ago that I rediscovered. It is awesome that the docs/pinouts still exist. As I wanted to use these with some newer hardware without too much hassle, I found some breakout boards for the connector used by the ribbon cables.
https://www.aliexpress.us/item/2251832836155784.html
https://www.aliexpress.us/item/3256808161896897.html
The description is “2743 Daughter Cards & OEM Boards SWD (2x5 1.27mm) Cable Breakout Board 10PIN 1.27MM JTAG TO 10PIN 2.54MM DIP J-LINK V10 11 PRO” but “2743 Daughter Cards” will get you some options. It is about $1.25 each shipped for quantity of 10, or $2.10 for one. The silkscreened pinouts won’t be much help to you 
If anyone has some modules sitting around that they have given up on, perhaps you can try to offload them or reuse them via this thread. Not so much use outside of prototyping these days, but things like the Crunchlabs Hack Pack (Arduino based) that I got for my kiddo can be expanded with what you may consider old legacy stuff. You can also grab some cheapo ESP32s and run nanoFramework. Pay attention to the 5v vs 3.3v pins…