There is but the cost is way, way higher from what I can tell. If I want a customized metal shielding with awkward shapes, I can just walk down to Shenzhen and have 10 people clamoring to make it. Does the US have the same?

Yeah, Orange County. They don't try to compete on price though, just quality and speed.

Maybe not 10, but my company (in the US) has relationships with several machine shops nearby (some within walking distance of our office) that do custom metal fabrication for us, and sendcutsend and xometry can handle more exotic stuff without having to ship it from Shenzhen. I think the bigger advantage of Shenzen is more for actually manufacturing at production volumes cheaply, although maybe if you need something really exotic? Custom metal fabrication is not a good example here, I have a neighbor who runs a custom CNC parts business out of his garage (said garage is largely taken up by his CNC mill).

Yes believe it or not in the US you can also buy things from fabricators in Shenzhen.

If time is of the essence, or rapid prototyping is needed, the shipping hurdle is a real problem. Going down the street for the goods vs having them go across the globe is quite a difference…

Time is often not of the essence when doing fundamental research.

Not quite, but sendcutsend.com is good.