When you land at the beach in Tortuga where the Shipwright is... as soon as you go through the Town Arch its the first door on your left.
There will be a L9-12 Sargent there - so bring friend with you if you cannot handle that level yet (you will have to kill him - he will attack you if you try to search the desk first)
As SOON as he's dead - search the desk. You get 30 seconds before 'another one' shows up and you'll have to do it all over again
