I am not aware of ANY US company who makes 510 connectors.
If you find one, let me know.
Its not like China can ONLY produce "soft" metal.....the manufacturers will provide what you have in your spec.
And here's a quote from the Provape reference:
"Parts - Machined right here in Monroe, WA. We use US-made stainless steel bar stock to produce the tubes, top caps, bottom caps,
contact pins, etc. Everything is done on our machines locally. No outsourcing."
Just because they don't sell them as connectors or wholesale them separately doesn't mean they don't make them.
They also sell a quality 510 to ego connector. Yes, it's pricey, but it is obvious when one sees one that it isn't the run of the mill connector.