Maybe the ones mentioned in the book are just the ones where the magic still works- there might be countless others that have ran out of magical "Juice", been vandalized, worn down by the elements over centuries, buried or submerged by geological activity, etc.
Such statues might not have any magical effects, but still have historical or religious value, or monetary value as antiquities.
There are factors which would make a statue easier to find though.
It might be built on a natural landmark. Like a rocky island in the middle of a lake, or on top of an outstanding hill.
It might be that the easiest path through the hex leads past the statue. Swampy ground, thick underbrush, or natural ridges all funnel traffic. The Isle appears to be mountainous and broken, so there will be few areas that are just plain woodland for miles in every direction.
It might be that roads (maintained, or likely ruined) lead past or to the statue.
It could be that the statue exerts a psychic pull on those traveling through the hex. Or a twisted 'fate' leads people to always happen upon the statue.
So some might be easier to find. Some might be smack in the middle of nowhere, or worse, deliberately placed in difficult spots.
It does go back to who (if anyone) built these statues and why. More statues indicates that they had quite a fondness for the things.