Yes, it was released around the time that the Mew-themed movie came out. It is not available outside of Japan and we don't have a date for when (if) it will be relased in the US, or anywhere else.
What I'm about to say is pure speculation, so don't assume I'm meaning truth here.
What I figure is going to happen, is with the release of "Lucario and the Mystery of Mew!", we'll be given some sort of method to obtain the Old Sea Chart/Map.
I want to say they'll be giving it out on an E-card, but I'm doubting it what with the E-Reader seemingly being useless with Emerald.
It is however possible, despite it all, but if that's not what happens, I assume they'll either set up kiosks in certain stores (ie EB Games), either in large cities, or whichever of those stores choose to participate.
My hopes rest with Diamond and Pearl's WiFi capabilities to recieve rare Pokemon, though.. =/
I have never been able been able to get any rare pokemon, so this really makes me upset.... Soo, I am guessing there is no real need to rush to get Mystery Gift for my Emerald before May thirteenth, then?