So I couldn’t find anywhere to get the SD card reader that people had been modding so I looked around for other options. It looked like something quite widely available that may fit are the Apple SD adapter knockoffs. They have the connector on a cable so not quite as easy to adapt but looked possible.
I’m definately no electronics or design expert but I thought this might just be within my ability. I’m sure someone with more skill would have done a much better job however if you really want an SD expansion card this is possible!
I ordered this one but wired the USB cable wrong during that attempt and it died… It was then out of stock so I ordered this one as a replacement. This was an extremely similar design but actually had smaller components on the PCB (leaving more space for cable) and it was an ever so slightly different size. I think you could likely have success with any of these. Just note the PCBs are slightly different sizes so you may have to redo the case.
Basically with a spudger I opened it up at the front, cut the cable and pulled the PCB out. I opted to strip the casing and sheathing from the cable and re-use that. I soldered a shorter length of cable back onto the PCB. I took the expansion card STL file and modified it in Tinkercad to hold the PCB and designed a top cover with a protrusion to hold the USB C connector from sliding back. It all went together with a little bit of tape between the connector and the board to make sure nothing shorts.
Below are the results, I’m pretty happy with it. I think it’s likely much less robust than the other option but hopefully it’ll work for a while. If anyone else is desperate for an SD module then this can be an option!