Any suggestions? Thanks.

Contact George at Viking Magic. He can answer your question.

Heavy white nylon fishing line. One I have is called FLY LINE BACKING. Get the heaviest you can find.

Kingry;
The "best" cord would depend upon the course that the cord takes with your sticks. All of the sets of sticks that I have made feature a tiny pulley at the top of the weight and metal eyelet entrance/exit points on the stick body - all to reduce friction. A twisted nylon cord like masons line will run smoother in most standard types of sticks. Sticks featuring pulleys and metal guides for the cord entry/exits can do well with braided cord (inherently has more friction). the "correct choice" here will vary with the sticks.
Jim

See if you can find some Spectra, either kite flying line or fishing line. This is braided, extremely strong and tough, and very slippery. The only problem is that you will need just a few feet and the stuff is usually sold in 50 foot and longer lengths.