A Deck of Many Things typically appears not as individual cards, but as a collection of cards characters can draw from. But this doesn't have to be true; you can give each card a property as a standalone item, so characters who find only one card can still enjoy this famed item and use the card on adventures.
This approach is particularly useful if you make a Deck of Many Things the object of a quest; as the characters explore, each card they find grants them a magical ability they can use in subsequent adventures to find the cards that remain. Eventually the heroes assemble the entire deck, which they can then use in the traditional manner, drawing transformative cards from it in a fitting climax to the campaign.