The Purple Banded Top Hat can be found on the first floor of the Clothing Store and purchased for 20 Bucks. Purchasing this hat will allow you to wear this hat only in Adopt Me!, unless you buy this item from the Roblox Catalog.
The description of this item on the Roblox Catalog reads
"This dapper accouterment is a symbol of wealth and prestige. Perfect for Victorian Balls and award ceremonies."