In Poland is hard to find a permanent place to purchase those cards, there are more individual charities - larger and smaller.
For example one in Krakow now:
We invite you to buy charity Christmas cards University Children's Hospital Foundation in Krakow "A CHILD'S HEALTH". The total income from the sale of cards will be used for the purchase of medical equipment for our hospital. Price Cards: 5 zł gross with an envelope.
szpitalzdrowia.pl/kartki-swiateczne-zapraszamy-do-zakupu/