>Pokémon encountered in the Friend Safari have a 1/512 chance of being Shiny, or eight times more likely than normal; this chance is unaffected by the Shiny Charm.
From what I got from this, I'm assuming that the number of Pokemon does not affect the shiny chance. Also, keep in mind, shiny Pokemon are pretty rare, you could be in a Friend Safari for days and find no shiny Pokemon at all.
Hope this helps!
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