Need Plastic Split Collar/Clamp for Telescoping Tubes

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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