Need Plastic Split Collar/Clamp for Telescoping Tubes

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I am looking for telescoping tube, collar clamps, made of plastic.  This has
got to be a very common item as I see them in use for a variety of purposes
from light stands to light bulb changers.  I have an old Norman light stand
that has no clamps and would like to get ones that actually fit the tubes,
i.e. 1/2"-5/8", 5/8'-3/4", etc.  Any help in finding a distributor in the
Los Angeles area or anywhere mail order would be greatly appreciated.  I
have been searching the internet for weeks with no finds other than a ton of
metal machine type collars made for space travel.  Here is a picture of the
clamp I am looking for:

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