Where to buy mounts, hinges, frame for the gadget?

Question

Robotics

I am assembling a gadget and I need metal mounts for an antenna and a case like this, but in a different configuration:

Where can I find connections, fasteners and hinges so as not to search for everything on different construction sites?
Maybe there is a specialized online store with a large selection?
If you know such a store in Moscow, please tell me what it is called.