Prusa i3 X endstop holder redisigned for a smaller mechanical endstop (12.75x5,75 mm). It counts with a gap that makes possible to fit the cables inside without unplugging the endstop from the electronics board. Now there is more space between the holder and the belt than the original Based on grkonrad's design: http://www.thingiverse.com/thing:158434/#files
Sorry for the late answer
These endstops came with my printer bundle from a spanish store (http://www.3despana.com/finales-de-carrera/309-final-de-carrera-mecanico-simpre.html)
I'm sure you can find some of the same size on ebay or other chinese buyers