These interesting items make up a Lock Laces kit. The idea is that you thread the elastic laces through your shoe eyelets, push the ends through the cord locks, and then through the cord caps. Voila! No more tying and untying shoelaces — just open and shut the cordlocks by squeezing.
They’re available from the rather stupidly designed website. You won’t be able to see a menu unless you put JavaScript on. (Don’t allow JavaScript universally, though, it’s a prescription for computer disaster.) (If none of that makes any sense to you, you’ve just illustrated why it’s so stupid to design a site like that!)
There’s a list on the site — if you can get to it — of sports stores around the country which carry Lock Laces.
Alternatively, buy the components from The Rainshed, purveyors of all kinds
of cool stuff. They carry elastic cording, cordlocks (to the right and left), and cord caps, all of which you can also find at some sewing stores and recreational/camping gear stores like REI, Eastern Mountain Sports, etc.
The Rainshed, by the way, also carries a huge fabric line — stretch fabrics, ripstop, polorfleece, microfleece, supplex, cordura, etc. If you’re making accessory bags for a wheelchair, a custom poncho, etc., this is a great place to order materials that might be difficult to find elsewhere.