As for me, most of my early day shinies were back when I first got my Gen III games. I never found any in G/S/C except for the Red Gyarados and R/B/Y didnt have shinies.
Barboach: Found in my Sapphire while fishing in Meteor Falls. iirc, this was my first 1/8192 shiny. I ended up giving this game too my cousin after he lost his Ruby and didn't have anymore Pokemon games. He ended up losing this game too :/
Oddish: Found this little bugger in the Safari Zone in my Emerald version. At that time I was doin an Ash's Hoenn team (Aipom, Pikachu, and I cant remember tne rest). I evolved into Vileplume and used it constantly. Later down the road, the game got soaked and was unplayable. I still miss the hell out of that Aipom I had trained. It was like lv. 87.
Spearow: This one was caught in Leafgreen right after I got my balls. Pokeballs that is. Went to go fight my rival with my lv. 8 Bulbasaur and found it. Used it in my whole playthrough. Ended up starting a new file.
Geodude: Also found in my Leafgreen. iirc, this one was found on Seven Island. All I can say about this one is good thing it didnt explode. Started a new file over her.
Voltorb: Again, found on my Leafgreen in the Power Plant. Again, started a new file.
Meditite: My first shiny in Gen IV. Found it on the southern most route from Snowpoint City in Diamond. Was pretty damn happy when I saw it. This is the game where I learned to chain and is kind of my shiny trove game. I got like over 150 chained shinies on it, but I rarely boot up that game anymore. Should trade them over I guess.