I bought the Kentucky Saddler and the Hungarian Half-Bred from a store in Mexico but for some reason the American Standard-Bred is not available. Does this mean I have to break it first? Please help.
Yes you have to break one first. It's really hard to find them though, at least for me it was. I found one while just riding around doing a bounty so you should bump into one eventually.
I'm sure there's a Youtube video or something that will show you good spots for them, if you don't want to wait
You have to break it to buy it later. They're found in West Elizebeth. I found a few south-east of Blackwater. Horse-breaking was easy for me, I don't see the difficulty in it o.O.