Wonder Guard is an Ability introduced in Generation III. It is the
signature Ability of Shedinja.
That's mean, there is no way to obtain Shiny Charizard with Wonder Guard, except if they do hacking, and this is more information for you.
Hackers often hack this Ability onto Spiritomb (Wondertomb) and Sableye (Wondereye), because those Pokémon do not have a weakness. Hence, they can be damaged only by status ailments, weather conditions, entry hazards, Fire Fang*, Future Sight*, Doom Desire*, Beat Up*, Struggle, recoil, Life Orb, Sticky Barb, Black Sludge, Rough Skin, Iron Barbs, fixed-damage attacks, after the use of Gastro Acid, Entrainment*, Worry Seed, Simple Beam, Foresight, Odor Sleuth or Soak, and by Pokémon with Mold Breaker, Turboblaze, Teravolt, or Scrappy.
This is the source. Hope this information helping you.