Although a normal joystick or USB interface works correct with RealFlight and RealFlight G2 (non-interlink version), you are not allowed to use RealFlight in such manner. Basically, the EULA (end user licence agreement) states that you are not allowed to use the software without the original interface connected to the PC.

The best option will be to send in your faulty interface for repairs/replacement at a nominal cost. You will not be able to buy a new controller alone. In my case, living in South Africa, it was faster to buy a new RealFlight package.