Praise be to Allah.
The scholars differed as to what items are subject to the ruling on hoarding. Some of them said that it applies only to staple foods.
Others said that it applies to anything that people need and they are harmed when these things are kept from them. This is the view of the Maalikis and is one view that was narrated from Ahmad. It is the correct view that is in accordance with the apparent meaning of the hadiths.
Ash-Shawkaani (may Allah have mercy on him) said in Nayl al-Awtaar (5/262):
The apparent meaning of the hadiths indicates that hoarding is prohibited, without differentiating between staple foods for humans and animals, and other goods. The explicit mention of staple food in some of the reports cannot be taken as making specific what is mentioned in general terms in other reports; rather it is by way of mentioning one item by name as an example of what is mentioned in general terms in other reports. End quote.
Ar-Ramli ash-Shaafa‘i said in his commentary on Asna al-Mataalib (2/39): The ruling on hoarding should be applied to everything that is usually needed of food and clothing. End quote.
This is in accordance with the wisdom behind the prohibition on hoarding, which is to prevent harm befalling people. Based on this view, the Permanent Committee for Ifta’ (13/184) issued a fatwa in which it said: It is not permissible to stock up on anything that people need, which is called hoarding, because the Prophet (blessings and peace of Allah be upon him) said: “No one hoards except a wrongdoer.” Narrated by Ahmad, Muslim, Abu Dawood, an-Nasaa’i and Ibn Maajah. That is also because of what that causes of harm to the Muslims.
As for that which people have no need of, it is permissible to stock up on it until it is needed, whereupon it may be made available to them in order to ward off hardship and harm from them. End quote.
For more information, please see the answer to question no. 85195 .
Based on that, if stocking up on these cards will not harm people, because they can do without them and use something else, there is nothing wrong with stocking up on them and it does not come under the heading of hoarding in that case.
But if not selling them now will cause harm to people, and make them face difficulty and hardship, because they have no alternative to them, which forces them to pay more than the usual price in order to obtain them, then this is hoarding and is haraam.
And Allah knows best.