The best place to find cards is in the "lost cards" bins that are sometimes in place at the change booths.

In fact I personally know of one enterprising slot token collector who was building these boxes himself and placing them at strategic spots around selected change booths and cages ... (something like setting traps)... and return to harvest his "kills" every early morning. Sorta like muskrat trapping in a casino. After awhile even the slot attendants and change people were dropping orphaned cards into these boxes thinking that the boxes belonged there!