I bought mine from the amazonian jungle website. Search for "Crystal Nail File" in their "beauty" section and you'll get a bajillion results. I went with one by "Fabulous Nail Files" as it had great reviews.
I like that it came in a handy case too because then it's easy to chuck in a bag / neck compartment of a case without it breaking or filing away something you don't want it to file away. After using it I just wash it with soap and water and dab-dry with a towel and it's good to go again for next time.
It cost me £10 - not cheap, but it is fabulous, daaaarling!
Negative, I am a meat popsicle.