Tom,
Some guys get them from RF Connection in Maryland. Sorry no part number or
url, but Joel has a good reputation and sells coax, connectors, and
grounding stuff. Last I remember (1 or 2 years ago) they were in the
$3.50 - $4.00 range. Perhaps e-bay, hamfest?
Shakespeare, who makes marine and cb antennas, has one for RG8X cable. West
Marine has them and I suppose others who carry marine/cb stuff.
Good luck, Steve KW3A