I got searching the other night for ideas on bulding a VP quad again.

One of the issues i had last time was finding a decent pitch slider mechanism. Well I found a few reasonably priced:
http://www.flying-hobby.com/kde-direct-align-trex-500-series-performance-tail-control-p-9740.html
http://www.flying-hobby.com/500esp-metal-tail-pitch-assembly-p-10400.html
http://www.helipal.com/h50189-500metal-tail-pitch-assembly.html

It seems the align trex500 heli pitch slider p/n is either h50189 or H50190. Should find out what the difference between them is.