Wago is a brand name that started the "spring clamp" style terminal block. There are several automation vendors that supply spring clamp or sometimes called cage clamp terminal blocks.
Unless the KOP regulates specific "Wago" brand, you should be able to obtain other brands in the same style:
Several names come to mind:
Automation Direct would be the easiest online store:
Spring Terminals
Allen Bradley offers Spring Terminals, though normally need to visit an Allen Bradley distribution house, such as in my area "Indiana" Wabash Electric, Kendal Electrical, Kirby Risk, etc.
Spring Clamp IEC 1492 Series
Phoenix Contact is another place to get Spring Clamp terminals.
Spring Clamps
Weidmuller is the Germany company terminal blocks.
Tension Clamp Style
I could probably go on and on....