Collect four chips (Green, Red, Cool, and a Superchip) to get the Casino. You get a chip for playing every day for five days in a row: on the 5th day you can choose to receive seven superbucks or a chip. Click "Receive" as shown below to obtain one of the four chips:
Once you collect all four chips, you will be able to receive the Casino from the daily bonus window.
If you've accidentally lost your Casino after obtaining it from the bonus window, it should automatically appear in your Storage.