Why do apricorns only appear in the mettalics regions??? If they're used to make special Pokeballs why aren't they in every game?

Maybe apricorns are only able to be grown in Johto, such as how certain fruits and vegetables are native to certain parts of the world. Besides, most of the Poke Balls that came from Apricorns were either gimmicky or had similar versions in other regions.

it is because many apricorn experts and ball makers are in thet region
for example mr pokemon

normal pokeballs are transported to pokemarts or pokemon labs.
some are even upgraded to make master balls and such like

ive just found out they are also used for apricorn juice only made in that region

(charizard) says tasty