This event was distributed to players at the New York Pokemon Center: Gotta catch 'em all! Station,
and the collection for various PCNY Pokemon ran across the period of November 22, 2001 to March 13, 2003.
The schedule of Pokemon changes weekly, and players was restricted to collecting one Pokemon per week per visit.
This Celebi has a 1% chance of being shiny, and the dates for distribution was:
December 21 to 27, 2001,
June 29 to July 4, 2002,
October 11 to 17, 2002,
November 22 to 28, 2002,
March 7 to 13, 2003.
A more comprehensive schedule list can be seen here.
DUE TO HAVING AN EVENT LOCATION,
THIS POKEMON WILL NOT BE LEGAL ON ANY VIRTUAL CONSOLE RELEASE.
Original Thread and Credits to Gold Ursaring!: