My first shiny was either a Noctowl or a Flaaffy in Gold or Silver. I found them both on the same route, the one below the lake with Red Gyarados, but at different times and maybe even different games (I had Gold, Silver and Crystal so I don't remember which game it was). I was particularly proud of the Noctowl because Ash also had a shiny Noctowl in the anime. Lol.
I never actually used either of them though, and they passed away a few years ago when the batteries of my Gold cartridge died... Sad times. So many treasured memories on that save file, and now they are just... memories. :( More than 300 hours of playtime... I get sad whenever I think about it, lol.