I remember staying at Caesars palace (before there was a Mirage). Caesars had two kiosks on the floor which serviced slot players. In the kiosks they also kept used decks of cards. If you asked you would usually receive 4 decks. Between my wife and myself that would be 16 decks. I would return maybe two more times during a 24 hour period as long as there were different workers. I believe the Sands and Dunes and possible other casino would also give away cards

I must have retuned home with 150 decks or more. I probably could have gotten hundreds more.