Distribution methods varied worldwide. In North America, the Eon Ticket could be transferred to the games through Mystery Events using an e-Reader and the Eon Ticket e-Card. In Europe, it was possible to get the Eon Ticket at promotional events, but it could also be downloaded through Mystery Events from special Nintendo cartridges via Game Link Cable.
A player that received his/her Eon Ticket from either the e-Card or a promotional event is able to share a limited amount of Eon Tickets with other players via record mixing. However, Eon Tickets received via record mixing cannot be shared further. Record mixing is the only way to obtain the Eon Ticket in Emerald.
A physical copy of the ticket was available through Nintendo Power magazine, volume 173.
tldr It's event exclusive.