As above; I have a career on the Irish flat schedule, big group races show on my schedule for Meydan, France and England. But only some big group races like the breeders cup only show for the USA.
No other group races show on my schedule for USA for instance I cannot enter the American triple crown.

This isn't really a technical issue so I'm going to move it to game mods. That is just the way the Irish schedule is programmed so you'll have to play the English (I think the original English one has the Triple Crown) or the American. Failing that you can use the schedule editor in game to make a new Irish Schedule that includes the Triple Crown and as many other overseas races as you want (to a certain extent). However, you will need to start a new game to use the new schedule so you'll have to transfer the horses you want from the old game into the new one. Those in the breeding barn cannot be moved.