Throughout the books and movies of Harry Potter we see lots of muggle outfits, when wizards go out in public their outfits are from muggle shops, how they get to these muggle shops is unknown, maybe JK Rowling will release an answer to these questions. We can only guess that Hermione got her outfits when she was in her hometown with her muggle parents. But where may I ask did Harry and Ron get their clothes, maybe their is a shop in diagon alley.