You could try to get the free one from FMS. Try this link:

http://www.microflight.com/FMS-Flight-Simulator

It is free. Keep in mind though, that although flight simulators are a very useful tool go get acquainted with RC flight, they are no substitute for the real thing. Only actually flying a plane can teach you how to fly it. A great alternative to flight simulators is to find a club and get an instructor/mentor to help you out. A lot of clubs have trainer planes for just that purpose.