Heres the source if you want to buy and start selling them.
McMaster-Carr PN 6567K52 for 1/4 inch hollow core with 6567K22 connectors
PN 6567K53 for 5/16 inch hollow core with 6567K23 connectors
The belting is about a buck or so a foot, and the connectors are $5-7 for 25 ea. Lots more on page 914 in Catalog #108. Bob Londress sold/gave away dozens of them years ago. The only thing to remember, is to roll something hard over the connector to lock it in the belt, and really pinch the other end very hard several times after joining, when in the pits. Have fun!!