Hmm. I would to use a sound program or mixer of some kind with just any native american chanting sounds and treat it with delay or echo.. Music programs are amazing these days.
Find the sample you want use and then using an audio editing program to reverse it. Add an echo or a reverb and then reverse it back to normal. That will give it a really spooky effect.
Yeah, if you can rent a delay unit, we did that using the patch called GATE which reverses the echo. Very cool effect, they used it in Poltergiest where the little girl was trapped in the other dimension.
I know the soundtrack to the movie "Smoke Signals" had lots of Native songs and such on it; don't remember how many might have been angry or spooky, but worth checking out.
(http://www.amazon.com/exec/obidos/AS...584801-7298458)