"The Eon Ticket can be received via StreetPass from another player who obtained it via StreetPass. As such, it can still be obtained via StreetPass. Since StreetPass data is exchanged with other people met via the PSS, including via the internet, it can also be obtained by connecting to the internet via the PSS, and can currently be obtained this way."
I think you can get it by simply being online, via the "passerby" feature. I never put my 3DS in sleep mode and it always worked for me, to just connect online. Eventually it showed up in my bag.