I'm not sure I follow. Carefully made whetstones long predate modern times, we find them in prehistoric sites, let alone ancient or medieval ones. And it's not as though you need a perfectly machined stone to sharpen a blade, any reasonably fine-grained stone with a good surface will work, especially since whetstones tend to become polished over time by the action of sharpening. My grandmother in Taiwan, for example, still sharpens her knives with naturally-occurring stones that she finds and it works just fine...