With the new horse update, I obviously wanted to get a horse in the world I play in, the old survival world. Apparently though, horses seem to be a little too rare in that world. I literally searched every plain in the world and only found one donkey. So I'd suggest an alternative way of getting horses, by either adding horse eggs to the shop or by adding a command to buy them to make sure you can only get horses in the old survival world. The price should obviously be high (1000$ - 1500$).