If you have shiny Eevee and specifically want a shiny Vaporeon... good luck! As per old research by the now-defunct website The Silph Road (via Wayback Machine), the shiny rate for Pokémon on a ...

During this period, players will have an increased chance to capture a shiny Eevee and its Eeveelutions ... will feature a larger number of Vaporeon, Jolteon, Flareon, Espeon, Umbreon, Leafeon ...