George:
I know exactly what you are talking about.
First, a little personal reflection...
In the summer of 1986, on a trip to Michigan to visit family, I came across a 1969 300 convertible in a wrecking yard near Grand Rapids. It had been there several years and was a bit waterlogged from sitting out in the Michigan environment. I did manage to save the moldly remnents of the original convertible top boot, which contained many of the plastic clips you mentioned.
Curious about their origin, I carefully removed one from the old boot. What I discovered molded into the plastic clip face, was a Chrysler part number, 2878583. In the fall of 1986, I went to the local Chrysler dealer parts department and asked them to run the part number. At that time, the part number was good, with stock indicated. I could have ordered as many as I wanted for 56 cents a piece. In a trip to the showroom, I soon discovered that four of these clips were used in each of the boot covers of the then, brand new, 1987 Chrysler LeBaron convertible.
What has truly amazed me is that I have never heard of anyone else discovering the part number of these little clips as I did, either before or after I did. I guess this have been my little secret for the last 28 years.
So, the best sourse I can give you is Chrysler. You may want to see if they are still available today. I still have that old boot, and I still have 15 used clips available.
Chris the K MANIAC