In the end of Chapter 2, Interlude, talk to Lloyd twice to enable the Trade Merchant menu in his shop. This option allows you to spend Libra to send Lloyd's contact to any part of the world to obtain rare items. The number of days it takes for the merchant to return and the cost of the expedition depends on the location. Take note that "one day" is equivalent to Arnice completing her day activities. Refer to this page for more information. Once the time is up, you'll obtain one of the two items you can get from the region you sent the merchant to.
There's also a skill called "Trade Cost Less" that lowers the expedition cost up to half. This is unlocked once Arnice reaches LV6.