Yes it is in the game. It is used for the special mission of Seraphine.
Where in the walkthrough is that. I did a name search for her and didn't find it.
Edit: Nvm the confusion came after the first won pony race. If you try to give her the pony costume again she asks for a stable holo card but no matter what trader you go to you cant find it and she doesn't need it to compete again.