What is the name of the pressed brass part in a plug socket?
There are many names for such elements: brass contacts, female connectors, female terminators, power plug connectors, electrical contact connectors etc. 

Plenty of these connectors, in various types and sizes You could find in Heyco: https://www.heyco.com/Power_Components/ Of course there are many other manufacturers of such elements, feed the Google with phrases like "power plug/contact/socket brass elements".

Another (in my opinion easier) option is to use complete PCB mounted power socket, like this one: