The premier stochastic oscillator as discussed in "Premier Stochastic Oscillator" by Lee Leibfarth is available for download here.
Once downloaded, from within the NinjaTrader Control Center window, select the menu File > Utilities > Import NinjaScript and select the downloaded file. This indicator is for NinjaTrader Version 6.5 or greater.
You can review the indicator source code by selecting the menu Tools > Edit NinjaScript > Indicator from within the NinjaTrader Control Center window and selecting PremierStochastic.