At one time, you could buy them from the cashier. Then casino policy changed, and it was strictly "no sales." I learned this when I returned to the casino one day with a couple of $3 chips that had no buyer interest on eBay. The cashier was very surprised that I had any and asked how I got them! I replied, bought from the window a few years back, and he said I was not supposed to have them. He asked if I had any more, to which I said, no. He agreed to cash them in but said that was the last time he could do that. So, it's unlikely that a lot of $4 chips are still floating around out there.