You can get both your bus sticker and readers at the AS Ticket office.
AS Program Board has a lost and found for things they find at all events they put on (concerts, Free Film Tuesdays, etc). You can go into there office and check if your belongings are there. There office is on the first floor of the AS building, down the hall from the Main Office.
Let the receptionist at Main Office know and they can log you out. Please remember to log out next time!