75 years ago AIUI light aircraft engines would run on the same stuff as commercial flights. So, since Amy Johnson etc were flying between existing airfields (mostly) there was fuel.
When I went to Australia in 1985 there were still DC3s around so there was avgas in many places though even then there was none at Jeddah and Rangoon.
The difficult bit with flying outside Europe today with a petrol light aircraft is fuel availability, it makes life much easier if you have a ferry tank and/or a range greater than 1000nm.
Flight clearance agents and ferry pilots often know the latest situation.
Sometimes there is a flying club and/or you need to know someone with some drums in a shed.