Howdy, I play around with atlatls too. I've read a lot of varying opinions on what the atlatl weights do. I'm not very good yet so my opinion may change, but while the weights do seem to make the atlatl feel more balanced, I have yet to notice any positive affect on performance ( distance or accuracy). They do add some beauty and 'medicine'.
Weights are easy to carve out of soapstone or catlinite.
As an aside, I made some takedown aluminum darts lately. Now I can carry a dart or two and an atlatl in my quiver, so I can make a few practice throws every time I 'm at the range.
Ron