Aluminium Upgrade Scroll Wheel Roller for Spektrum DX6i Transmitters
http://www.hobbyking.com/hobbyking/store/__29799__Aluminium_Upgrade_Scroll_Wheel_Roller_for_Spektrum_DX_Series_Transmitters_Red_.html

Get one cut from local machinist though you will require some dimensions, you can probably get it for 100. If not use the plastic scroll wheel with a custom metal jacket covering it.