Update: Trainers, Shiny Teddiursa is now available worldwide.
Previous Story: Trainers, shiny Teddiursa and Pikachu wearing a hat are now available in the game, but only for Safari Zone St. Louis ticket holders.
Only players that have a ticket to the Pokemon Go Safari Zone St. Louis event will see the Shiny Teddiursa. Due to the situation, this event is postponed, but the good news is that the ones that own a ticket will have the special benefits that were told the attendees will have. These benefits will start at the originally scheduled hours in their time zone (from Friday, March 27, to Sunday, March 29, 2020).
If you have a ticket, you should be notified by Niantic about the updates, meaning that there will be no action required to participate in the gameplay.
That being said, Niantic and Pokemon Go activated the Safari Zone Pokemon encounters and Special Research globally and players are reporting of Shiny Teddiursa and a new Hat Pikachu through Special Research.
— Kelven (@Kelven91) March 26, 2020
NOTE: Only people who purchased tickets and kept them will receive the spawns.