In Ruby and Sapphire, there was a problem with the berry system, so after a year or so, berries would stop growing. So Nintendo put a patch to fix it in Colosseum, Box and some other games. And the patch had a shiny Zigzagoon attached as apology.
Was that just in the american version? or was it in the europeon versions as well?
Anyway, shinies that i've found in the third gen were
Ponyta, Found while looking for a magmar in leaf green for my pokedex
Wurmple, Found it by racing through petalburg woods in sapphire
Sandshrew, I was looking in the desert in sapphire hoping to find a shiny, shiny sandshrew was the sixth pokemon i encountered
Wurmple, Found it ev training an umbreon in speed in emerald
Abra, Soft resetted at the game corner for many months until i bought a shiny abra.
Shiny zigzagoon, This one i'm quite proud of because this particular zigzagoon is the extremespeed zigzagoon you get off pokemon box, i was just hatching four random eggs i had in my party and BOOM, this was the second egg to hatch.