Story Dream Projector Cartridge Holder
Designed to be able to hold 21 cartridges and 3 of the characters. Each slot has a 10° angle so the cartridges don't fall out too easily and there is enough wiggle room that kids shouldn't have issues putting the cartridges in it.
If anyone wants different sizes for it please leave a comment and I can try to upload more options.
Link to the Story Dream Machine to go with this https://amzn.to/4sg2GL5