Post any seeds you find that have horses! Put in the cords if they are not in an obvious place. Take into consideration horses DO despawn if they are not tamed. So I'd recommend taming the ones you want, and then come back later with horse saddles (Or find regular pig saddles to prepare for when the horse saddle is removed)
Here's one of the more popular ones:
There are horses everywhere in this one. Most notably to the left of where you spawn.
Cords: X: 56 Z: 270