The lever mechanism I used in this credit card holder is well known in the magic world and allows for good card retention without the need for additional springs.
To connect the hinges, metal wire 1-0.8 mm is used. Since the parts are small, careful post-processing is required. All hinges should rotate easily, but the ends of the wires must be bent or thickened in some other way.
https://youtu.be/WMbyU8N4RHM