First off, can you see it under your installed items? On mine it usually shows up under Objects instead of Lots in the launcher, but either way confirm that you see it there. Is the world itself installed, but the casino lot is not? I am not sure if the casino is automatically installed in the Lucky Palms world or if you have to place it. I bought them separately so I had to actually place the casino in the world via edit town.
If it is not in your installed items, try downloading and installing it again and see it that does it. The casino itself should be in the Community Lots bin when you go into Edit Town.
You should also check and make sure that the objects that would have come with it are appearing in your game. Check under Entertainment - Misc. in your objects catalog in game and see if you see the card table and the slot machine there, as they are the easiest to pick out.
Another thing you should check is any mods or CC you have in your game. Although that normally wouldn't prevent items from showing up, sometimes a bad mod can cause all kinds of craziness in your game.
