I decided i was sick of carrying around loose 3ds cartridges in the drawstring bag I got from club nintendo a while before it was shut down. Here's my solution. It's very similar to a ds game case I had when the DSlite was current. This case has 12 slots and 2 extra stylus holders.
The hinges are designed to use 3mm filament as hinge pins.
Depending on your printer, you may or may not need supports for the hinges.