I know of at least three casinos on the Mississippi Gulf Coast that use over-sized "Promotional" chips -- The Island View in Gulfport, The Isle in Biloxi (They just started with a yellow and white chip) and the Silver Slipper in Hancock County at Lakeshore, MS.
The Silver Slipper has three different colors and denominations ranging from $5 (Blue), $25 (Peach) and $50(Lavender). I have the first two levels of their "promotional" chips, and got a second peach-colored one over Christmas.
To get them, you must redeem a coupon that comes in a mailer at the cashier's cage.
However, they must be used in connection with a like amount wager on even-money bets on certain table games. Once you put it down with the same amount of money chip, the chip disappears into some strange hole. It's never seen again. If you win, they give you regular house chips and the "promotional" ones disappear.
Depending on your level of play and card status (gold, silver, platinum) determines the value of "promotional" chip you get. At the Slipper, I go to the poker room where the regulars play and offer to buy them for $5 each until I get enough to cash up to the next level chip. I am working on getting enough for the lavender chip. Hope this offers some insight into how this works.