I'm sure if you have a large population you dont have to drag everyone, within the first ten your likely to have a chief.

It's not a percentage chance, unfortunately. One villager is the chief, and that villager is the chief, and only that villager, even if he or she hasn't been robed yet.
That means if I have 100 villagers, I have a one percent chance of getting a chief - just grabbing ten at random only gives me a one in ten chance of a hit. In cases like this, there's just no way except to work methodically.