Prather Products used to package those, but I don't know if he is still in business.

However, you can get them from Aircraft Spruce.

http://www.aircraftspruce.com/catalog/hapages/dzus.php

The small ones work well if you make a retaining ring from the 1/4 soft copper washer from a glow plug. Also to work well, the fastener needs to engage a springy loop of wire.