The inventor of UPC, George Laurer, can't even get a list, even though he has tried for years.
I then contacted a friend of mine from grad school who does business research for a living and who has access to very relevant databases and he
couldn't find the information either.
One thing that might help my client is if he
can find a list of the companies involved in the class action suit levied against the GS1 in the state of Washington.