There are a couple of possibilities:
1. It's a custom or homemade game: Perhaps "Horse-opoly" is a name given to a game someone created themselves, based on the classic Monopoly game.
2. It's a lesser-known game: It's possible there is a board game with that name, but it's not as popular or widely distributed.
To help me understand what you're looking for, could you please tell me:
* Where did you hear about "Horse-opoly"? Did you see it in a store, online, or was it mentioned in a conversation?
* What kind of game do you think it is? Is it a horse-themed version of Monopoly, or something else entirely?
With more information, I can hopefully help you find the game or figure out what it might be about.