You can't buy an interface cable for Reflex, you have to buy the sim to get it, that's how the copy rights are protected
If your having problems with your's, just send Reflex an email and tell them your problem and they mite sell you one, but I'm sure they will want to see your prof of purchase (receipt) for the one your having problems with, or they will get you to send it in to them and they will replace it.