There are about 14,000 helicopters registered in the USA so double that and you have a figure close to the 22,000 registered helicopter pilots and not a million miles from the German figure listed below by Goodgrief.
So I would multiply by 1.5 then by 2 the world helicopter fleet to get a possible spread.
How to get the figures?
Rotorspot
ROTORSPOT - Rotorcraft Registrations Database (Worldwide) has current registrations for almost every country with a total for that country at the top of the list.