
LizardMage |
Pathfinder Lost Omens, Rulebook Subscriber

The number of dragons is X+1. X=The number needed by the GM for the adventure or backstory of each character and backstory to the adventure. +1 because of the gold dragon that rules the eugenics experiment nation.
Not being a smart ass, to your question but really Dragons do not seem to be so rare that you could number them down to the hundreds or so.