A simple angled card holder. I've uploaded three versions (10cm, 12.5cm and 15cm) to suit your needs. 12.5cm is perfect for Hanabi (or other games which require you to hold four cards). I would recommend the 15cm version for 2-player hanabi since that requires you to hold 5 cards.
Models in picture printed with 15% infill, standard shell thickness and 3 micron layer height.