i believe they are sold at Home Hardware as well, just look in the electrical section... home depot has them as well....
if u cant find these particular ones u could use cord seal connectors which are basically the same except they tighten around the object inside of the connector as u tighten it
if u cant find these particular ones u could use cord seal connectors which are basically the same except they tighten around the object inside of the connector as u tighten it