you should be able to grab one just about anywhere on the fretboard... it's all in the fingers.

Let's just be clear about this. To do a regular harmonic sound like you do when you tune your guitar is where you lightly touch the string while picking it. The pinch harmonic is when you actually fret the note and then the harmonic comes from how you strike the note. It's almost like you're grazing the string with the tip of the pick and then hitting it with your thumb. I still can't get em' all the time and I've been at it for a few years now... (maybe I just suck) who knows.... :D