This unisex outfit can be produced in St. Petersburg at the City Girl (found on the way to the item shop from the bank) if you have the Adept of Ages (18th Century-P.3) title or are wearing Age effect (18th century) EX Effect equipment.
It can be enhanced with transmutation alchemy into Kaftan EX -- which one of only three items in the game which can possess the Age effect (18th century) EX Effect. See the linked pages for more details. Cheers.