I have Latios and its mega stone. I have a Latiasite too, and I wish to get Latias with the Eon Ticket. Therefore, I turned on Streetpass and so far I found no ticket. From what I've learned you need to pass someone who has the ticket. If anyone knows who they are please tell me.
"From what I've learned you need to pass someone who has the ticket"
This is pretty much it. The Eon Ticket started off with around 10 people receiving a physical copy of it, which can be downloaded into the game. Through StreetPass, if you pass someone holding an Eon Ticket, you will receive it. It's like a plague.
According to Bulbapedia The only way to get an Eon ticket is by attending an event
EDIT: There are some ways if you live in London & New York City
I don't know if it still works, because something changed with the latest update. People say that Nintendo resets the StreetPass relay servers with each update. Another reason could be that the very major point release of the firmware makes systems on the new version unable to streetpass systems on the old version, and it takes a while after the update initially goes out for everyone to get on the new version.
Give it a few days and it will work again, I hope.