The maps aren't in the chests (If I remember correctly) so you have to go to a tavern, talk to the barkeeper and keep getting information until you get the location of a cadaver, go to it, get the map, check if it's what you want (in this case elite fire barrel storage), rinse and repeat.
At least that's how I do it anyway.
You cannot access the map in an other way. If you cannot access the Kenway Fleet, check the connection. I had that too the first time I played the game and was not saved in Uplay (as Uplay actions) or in the Iniitates