Premium Items are purchased from Leticia, Cash Item Merchant. She can be found in any major city, often near the Waypoint. The terms "Premium Item" and "Cash Item" refer to the same thing: items bought using Gold (i.e. real money). Some of these items are tradeable, which means they can still be bought with Vis from other players.
Premium Treasure Chest Edit
Polishers can be given to a Pioneer Support Soldier in exchange for powerful equipment. The trade-off is that this equipment cannot be traded to other players, and the amount of Polishers required for a specific piece of equipment increases with each trade.
Manuals come in three varieties: Combat Manuals, Tactical Manuals, and Survival Manuals. The first two can be purchased from the Premium Item Merchant, but the Survival Manuals are currently only available as rewards from special events.