Stayed at the Palazzo over Christmas.
They have a little gift shop and I bought some there.
I think they were $2.
I would think most casinos have a gift shop...
Like mentioned, most casinos will have it at their gift shop. If you are near downtown, go to "Gamblers General Store" for a variety of casinos used cards. You can also order them through their site: https://www.gamblersgeneralstore.com/cards/used-casino-cards/