since the Surface RT wasn't a big seller, and software for it is only available through the Store, chances of getting a file recovery program are probably zero.
if the files are important enough, and I have no idea if this is even possible or if it will wreck the Surface, but it may be possible to pull it about, remove the flash storage and connect it to another device for retrieval. lots of 'what ifs' with that option and it all depends on the importance of the data lost.