In the daytime, once you are out and about looking for those items that are missing from the bulletin board (in the 7th floor) common room, you'll get access to the Confiscated Items Storeroom in the middle of the Hogwarts grounds (using your broom) for a 200 bean holster. Once you get the key, fly to the center of the grounds towards a bridge and head towards the door. Open the door and you'll find one of the (five to seven) chests in that room with the 200-bean bag holster. Even after you save, you can still go back to the room and get that bean holster even when you're low. Once you get it, you'll have 200 beans, and you don't even have to walk around finding any more!!!