Answer:
trading cards
Step-by-step explanation:
A hockey card is defined as a trading card that is typically printed on some card stock. These cards features some hockey relation editorials or images of ice hockey players. It is mainly found in the countries were hockey is one of the popular game such as Canada, USA, Sweden, Finland, etc. People are huge fan of this sport and they collects these cards for passion.
In the context, Billy went to a store to buy some hockey cards and there were not many hockey cards in the store. These hockey cards are the trading cards which features the most popular sport, 'hockey' on their cards.