It depends on what sort of fringe you want. Using wool yarn will make very light fringe that when long tends to clump up. Using synthetic yarns (nubby, feathery etc) will make long looser fringe with good movement. The smooth synthetic cord/thread (which I think is probably what you're thinking of) are usually polyester and will make swaying highly mobile long fringe. Usually this stuff is bought as a fringe already, by the yard in what ever length you like. Try a google search or ebay. This stuff does look modern so if you're going for a more natural (I won't say authentic since tribal dance isn't authentic to any time, culture or what have you) look then you might want to avoid this stuff.
I don't usually attach the longer base fringe to the main belt, but make it a seperate one. That way the belt can be used for several different things. And sometimes its just damned inconvienent to have all that fringe draggin around. Nice fringe only belts can had for usually forty five to eighty dollars depending on length and dye job.
If you can give a little more clarification of what you're interested in I can post some links for you.