How to get the american standard bred horse on red dead redemption.?

I have more than enough money and i have beaten the the game but it says that it is unavalible.|||You have to wrangle the horse first before you can buy it. Look for a pure-black horse in and around the Great Plains and lasso it. Then break it and you can then hitch it to save it as your horse. You can buy the horse in a general store for $750 in case the one you took dies.