I get the whole point of playing legitimately and all, but sweet baby Jesus nobody in their right mind will blame you for just giving up and Gamesharking that shit after the 10th cycle. Shiny hunting has got to be in the top 5 most retarded things people do in video games overall.
Hell, their genetic line might have ended up somewhere else in the world, given how Pokemon's loosely based on Earth and I figure the existence of new Pokemon in newer games is just a silent retcon, because how else can you explain that they managed to figure out genetic manipulation before discovering Hoothoot, because nobody ever thought to drive south for about an hour
Maybe all the Hisuian Growlithes got traded away to Westerners during the Opium Wars and they all ended up in Pokemon's equivalent to Boston. I dunno.