What I know that are Costar: Das, WASD, Steel series, Thermaltake, Ozone, Mionix
CM is not identical to Filco. Single layer PCB, different case, LED indicator in keycaps etc.
I asked someone about Ducky, and they said it was Costar.
There are conflicting reports on Leopolds, but it made in Taiwan. Some guy on a Taiwanese forum said it is Strongman, but Strongman has been out of business for couple of years. I guess right now I wouldn't be surprised it is a Costar seeing how many different boards they manufacture.
Zowie is made in Taiwan... Costar?
Noppoo, PLU, and Razer are made in China. Don't know the OEM.