There is also Hairsellon.com which I prefer over buyandsellhair.com. You don't have to pay to be a member and there seem to be more frequent ads.

I also have a ponytail collection of my own that I might be looking to sell off soon. I actually haven't really touched most of the ponytails that I bought and they're just stored safely away waiting for the right person to use them. Email me if you're interested and we can talk a cheaper price than what you probably would find on the sites.