I just poked around a bit, and found that the beads used actually are, as I suspected, the same as the clear beads used in flower decorations (also some kids' toys but the name escapes me, and even some active humidification systems though more often home-build systems replacing more common foams). They're REALLY cheap, and if you're interested it would be very easy to make your own 'kool tie.' Basically just sew the beads (if dry, with enough room to expand when fully hydrated) with a tight enough seam that the dehydrated pearls cannot fall through. But there are some slight concerns:
If the beads degrade when dehydrated, avoid any ingestion of the dust (or gel). They may not be silicate based, but they're not that good for you. Also, I recommend distilled water, as anything dissolved in the water will remain behind, eventually clogging the absorptive properties. But that shouldn't be too fast so it's not a GREAT concern, as I doubt the beads will remain intact with very frequent use.
The big advantage of the beads, over just wetting a bandanna, is that they hold a lot more water than just the cotton cloth, which provides prolonged evaporative cooling.