Hey Martin,
when I search for “aviation connector”, how these are commonly called, but it is not a technical term, I find lots of these but also with the same problem: Their maximum cable diameter is not large enough. This may be the case because these connectors are not power connectors, or at least not for such high currents.
If I search at mouser.com and digikey.com, you maybe know that they have tons of connectors, and many without images, so this would be a search for technical data only.
For a quick search on mouser.com I chose:
Standard Circular Connector
Contact Gender = Socket (Female)
Number of Positions = 4 Position
Product = Connectors
In the web, it is easy to find the connector that you show (example) or at alibaba etc., but they all have this problem: They are only for smaller cables.
On CNC forums, I saw persons who share my opinion that one could exchange both the socket and the plug. There is a reason why Mechatron does not make spindles with these connectors anymore and switched to Phoenix M17 instead. But M17 are more expensive and you need the four-mandrel crimp pliers for turned contacts, and you need to exchange the socket on the spindle too. The advantage is you don’t need to solder.
However since I never had such a connector like you show and never needed to search one, I am not sure if I am the right person to help you. Maybe people at other CNC forums know a source for a connector matching the one on your spindle, but for thicker power cables.