If you don't want to gather most of the wizard cards going around the school and looking for those chests, get like 1000 sickles and go to Fred and George in the southeast part of Floor 7. Go to "BUY" and then go to "MISCELLANEOUS(?)" and buy like 200 Chocolate Frogs. You might even get at least two of all of the cards in a card combo. You also want to get these cards to go to the west room on Floor 5 to unlock prizes and stuff (when you have all of them in a particular category; ex: Quidditch).