I know a few guys who have been taken on by CHC Global and were told that they could not work in their home countries.
This as it was explained to me has mainly to do with the salaries they earn and the rostering system (6/6) as it would cause friction with the nationals if they were on the floor with their countrymen earning more and on the expat roster.
ETB, my apologies for assuming you were expat. Like Swamp 76 put it, you would first need to join up with Global/Bristow/Heli Union/whoever then dependant on your types/experience etc etc the world would be your oyster.
It's a different and sometimes difficult life, but IMO it beats the Monday to Friday 9-5 gig hands down.