I think you'll need to contact RealFlight about this. Was it ever loaded and registered? My suspicion is that if you registered it, or can prove via a receipt or something that you did indeed buy it, they may provide you with access to the software. Since you must have the adapter cord for it to work with your tx (you do still have that don't you?) they may be pretty open to providing it to you. If it was never registered, you don't still have the cord or a receipt to prove you bought it, I'd say you're probably out of luck. Only one way to know for sure and that's to get in touch with them.

Other than that, I don't see another way to do it unless someone is willing to call tech support, "un-register" theirs and sell it to you, or get a full G3.5 system which has the Nexstar in it.

If you're going to continue in RC stuff, the full program will save you a bunch of money on models you won't wreck because you had the sim to practice on...