Gil Farmer augment is located in Troia town. To gain access to where the augment is, you'll have to buy a ticket from  a lady in the INN that costs you 100,000 gil. That's a lot of money, right? Well, if you don't have enough, you can just sell Megalixir. Don't worry, I know Megalixir is super super rare but you can farm it later from Proto-Babil as many as you want.

Once you get the Member's writ, go and watch a show. After it finished, go the dressing room and pick it up.