Someone in town might be able to sell you one.
In fact, the Citizen of Melee in the central part of town can sell you one.
He tells you about his cousin named Sven.
He's naming random people.
So maybe you should name a random person.
Tell him about your barber Dominque.
Remember, you want him to give you a map.
Ask to buy a treasure map off him, and he'll say it'll cost you 100 pieces of eight.
I need some money!
Give the money to him, and you've got yourself a map.