Here, elsewhere online. my little wiki will show other countries versions of a US pony when people donate information and pictures.
It's a learning curve sometimes to be able to spot them in the wild. Sometimes the differences can be very subtle. As you learn more one thing that can be helpful is making your own list of identifying features for various countries. NOT just hoof stamps. So if you spot something in a lot, referencing the correct info is faster until you can simply do it by eye and memory.
"in the wild" from a generic re-seller, I don't ask too many questions if I think there is something special hidden in a lot. I bid for what I know 100%. So if the common version of that pony is only worth $7, maybe a bit higher is my cap. too much interest for one item often gets the listing ended early, and that pony listed separately, correctly ID'd for more money. Same can happen in irl with second hand vendors. play it cool. (original owner, or a pony collector themselves though I am nicer and let them know if I think they have something special!
In my mind though, buy cheap sell high flippers should be doing their own research)
Variants there are also seemingly endless possibilities with new ones turning up all the time. I don't know if this was helpful at all, but best of luck.