From my own experience I can tell that there are only a few famous brands to look for.
Most US shears came from Newark, New Jersey. They are all similar in shape and the most renown are:
WISS & Sons
R. Heinisch (Inventor)
Equity
In Germany were: Kissner, Gross Umstadt and of course Zwilling, Solingen. Plus a few others like Rich. A. Herder(Solingen)
In France shears came mainly from Nogent, mostly in only a few shapes(still available today)
In the UK most famous is Wilkinson & Sons, Sheffield(the only company still making 13" shears).
Here is a picture of my "collection"! They are all! in good to excellent working condition!

Here is a picture of the largest ones I have:

They are from the manufacturers mentioned above:
Left to right: R. Heinisch, Wilkinson, Nogent and Kissner.
Found them all on Ebay in UK, US ,France and Germany.
SG