https://github.com/MiniblockchainProject/CudaMiner
There are several things to keep in mind 1) it is designed to work with 700 series nVidia cards but should work on 400 series cards if you change the make file 2) for now you will have to compile the GPU miner yourself for various reasons, we will try to post pre-compiled binaries when they become available.
See github project page for more information about usage and compiling.
Don't like the idea of gpu miners getting in this early, but it's eventually will happen with all coins that get popular enough. Good thing, it will prevent botnet from monopolizing the network. Hope an AMD miner is in the work.
Will there be a product/service that can be use with XCN? I mean purchase things with XCN exclusively.