Take a look a the following using a "LittleBone" TM
=
Nice gadgets for leveling as well.
http://www.ebay.com/sch/understringguitartool/m.html?_nkw=&_armrs=1&_from=&_ipg=&_trksid=p3686
Also You can buy proper diamond files from Jewelry fabrication supply stores such as
http://www.reefdiamond.co.za/strauss_industrial_diamond_tools.html
Hope this helps