Where do you find arago in tom riddles dairy Lego Harry Potter?

You won't find Arago in Lego Harry Potter: Years 1-4. He's a character from the later books (Harry Potter and the Goblet of Fire) and doesn't appear in the games based on the first four books.

The game features characters and locations from the first four books, so you'll encounter creatures like Fluffy, the three-headed dog, or the spiders in the Forbidden Forest, but not Arago.