For this achievement (and Commendation Master Cartographer) you'll have to bury treasures on different Islands, thus creating treasure maps and turn these in to the Quest Boards (found close to the Merchant Alliance at any Outpost or at any Seapost). Grade V comes down to a number of 25 maps.
You can combine this with another Commendation Hider of Sizeable Stashes, which reads You created a Treasure Stash map that leads to five treasures on the same island. Hide 5 treasures on different Islands, creating 25 maps and turn them in to unlock both Commendations. This works towards the 100 G 'final' achievement Beholder of Buried Treasures.
Note: I'm not sure, but I have heard that you can only donate 5 maps per day. What I do know for sure, is that you can only buy 5 maps per day. Try it out!