To get the horse, go to mission 37 (The End). After destroying the drones, go up , then turn left and then go to the right section of the Crusher. Go ahead, then you will see a horse icon on the corner. Drive over it to collect the horse.
to get a horse you must be at the final boss then look at the left or the right there will be a horse icon i think then drive to it to collect it if you dont know what am i saying go to shockwave Burnin Rubber 5 to see all the comments