You aren't the only one. Ubisoft got some problems with keeping the online servers up and running.
You can see their twitter account for news about the situation. As you can see it's full of "it's working - it's not working - it's working again - oops, it's off again" messages.
Best Answer
It unlock when you reach the second island. You can also unlock the signature version when you find 20 relics that fires explosive rounds.