>>48348209I have encountered at least one non-scripted shiny in every game I've played without looking for it since gen 2
yellow magikarp south of pallet town (silver)
blue beedrill in the bug catching contest (crystal)
blue tyrogue in a random egg (crystal)
green wingull right before reaching evergrande city (emerald)
yellow rhydon inside stark mountain (platinum)
green tentacool in route 32 (soul silver)
yellow geodude in route 45 (soul silver)
yellow sandile in unova route 4 (black)
navi blue golduck in a dark grass patch in unova route 11 (black2)
blue mienfoo in kalos route 8 (Y)
blue zangoose (female) in a seviper horde in kalos route 8 (Y)
brown starly in a horde in kalos route 11 (Y)
green pelipper in route 124 (alpha sapphire)
green spinda in a horde in route 113 (alpha sapphire)
green zubat in a horde inside meteor falls (alpha sapphire)
gray alolan rattata inside verdant cavern (moon)
green primeape in poni wilds (ultra moon)
I'm sure there are more but these are the ones I can recall on top of my head